# CO2 revelations part 2#



## BlueRam (Sep 21, 2004)

Thanks Tom for putting a summary together. 

Good work!


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## plantbrain (Dec 15, 2003)

Well, hopefully is will show that both difussers and reactors are both good methods and that the mist can help later in the day after reaching 30ppm.

The method work with, not an either or type of thing with dissolved CO2 in water.

But I think there is fairly clear evidence now that CO2 does not dissolve nearly as easily after it builds up good.

The rate of dissolution at 3.7ppm vs 30ppm is different.
That would explain the bubble presisting and still being CO2.

Thus the mist can help even if you have 30ppm in the water, which is what I suggested originally.

The venturi loop I add to my internals and now can be used on any external reactor also helps reactors perform better and the current using the Disc also helps better.

In all cases, there is a better understanding and improvement as well as another completely ignored delivery method.

So no matter what side/method you use, this knowledge will help and improve the understanding using CO2, which, given it's importance, is extremely important.

It also adds yet another layer to improve growth and CO2 dosing.

Regards, 
Tom Barr


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## StUk_In_AfRiKa (Jan 30, 2005)

plantbrain said:


> My mistake in the past was assuming that the gas in the tube was O2, it's not, it's CO2 excess that's much more difficult to dissolve.
> 
> Thinking about the internal venturi reactors has shown that it cannot be O2(why would it degas there just like in the external sealed tubes)?
> 
> I tried this without any plants(thus no O2 build up), I had gas build up later in the day, thus reduction in CO2 dissolving at higher ppm levels.


I've been following the discussion and I grasp everything, except that. I don't have a degree in this subject so bare with me  Even if there are no plants in the tank, the DO would still be around 7 or 8 ppm at sea level. Since the bubbles are pure CO2, other gases would want to dissolve into the bubble. When the CO2 concentration is low the CO2 dissolves quickly and other gasses that take longer to dissolve don't get a chance to move into the bubble. But as the CO2 concentration increases and the CO2 bubbles remain in the water longer, other gasses would have time to dissolve into the bubble. So wouldn't this still mean that the "stubborn" air in the reactor is a combination of CO2 and non-CO2 gasses?


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## Hypancistrus (Oct 28, 2004)

> So this means, and I know I'm right(rare), that the CO2 dissolving is greatly reduced later at a styable given CO2 dosing rate in the day after you build up to a certain level. What level? I'd guess about 30ppm.


My reactor1000 always filled up to the top with water when I initially turned CO2 on, then after a few hours would develop gas in the top. I've always wondered why. This must be it.

Today after I disconnected my CO2 from the reactor and hooked it up to the diffuser disc, I didn't disconnect my reactor. I just plugged up the top where the CO2 used to go in. No more gas build up in the reactor!

So what I am seeing here does follow what you are saying.

StUk_In_AfRiKa, because the reactor is a sealed unit. Water is being forced through it at pressure. You also don't get air pockets building up inside the cannister filter, UV unit, etc., due to O2 degassing. The reactor has the CO2 being directly injected into it. Tom is saying that after the water reaches a saturation point, the CO2 that is being injected into the reactor stops dissolving and forms a gas pocket. When using a diffuser disc, rather than form a gas pocket the tiny bubbles get blown around the tank and onto plant leaves.


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## timr (Mar 23, 2005)

So all i might need to do is turn my reactor upside down and move my spray bar to the bottom of the tank? This may not get the co2 extremely small, but i know the spray bar does a good job of chopping up air that gets caught in the canister.


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## StUk_In_AfRiKa (Jan 30, 2005)

Hypancistrus said:


> StUk_In_AfRiKa, because the reactor is a sealed unit. Water is being forced through it at pressure. You also don't get air pockets building up inside the cannister filter, UV unit, etc., due to O2 degassing. The reactor has the CO2 being directly injected into it. Tom is saying that after the water reaches a saturation point, the CO2 that is being injected into the reactor stops dissolving and forms a gas pocket. When using a diffuser disc, rather than form a gas pocket the tiny bubbles get blown around the tank and onto plant leaves.


I've only seen pictures of reactors, but when the CO2 concentration is high in the water then the CO2 bubbles remain at the top of the reactor for a while right? So with all that churning wouldn't other gasses (even small amounts) still dissolve out of solution into the CO2 pocket? I know that if no CO2 was being injected then the O2 wouldn't degass, but if the CO2 creates that big bubble there then gasses would want to equalize and dissolve into the bubble. And if the air pocket in there is CO2 along with other gasses, then it would also contribute to the "stubborness" of it to dissolve (because the CO2 is less oncentrated in the bubble) right?

And I'm sorry if I'm confusing anyone with all this


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## anonapersona (Oct 19, 2002)

Hypancistrus said:


> Tom is saying that after the water reaches a saturation point, the CO2 that is being injected into the reactor stops dissolving and forms a gas pocket. When using a diffuser disc, rather than form a gas pocket the tiny bubbles get blown around the tank and onto plant leaves.


So, why wouldn't you just turn down the gas a bit? OK, gas is cheap, yes, but after the water reaches saturation point, you can either let gas build up in the reactor, or blow it around the tank as tiny bubbles. Either way ought to be the same... the water remains at saturation. 

If the glass is full and you keep pouring water into it, do you really care if it pours over the top into a sponge or down the drain? The glass isn't going to be any more full either way. True the sponge (gas bubble in the reactor) may keep the excess there for later, while the other way just makes the glass wet and in a way oversaturated. 

I think the more important point is that it is actually hard to keep the tank at more than 30 ppm. 

Seems to me to be overkill, no matter what. 

Anona, back from a second trip from Houston to New Orleans, this time through TWO hurricane wrecked areas, and reeling from the damages seen.


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## plantbrain (Dec 15, 2003)

Hehe, 

Unless you have seen the difference doing this method does to your plants and the pearling, you cannot really say too much about it not being overkill or not.

That same arguement can be posed for non CO2 vs CO2.........

Once you see the vigor and growth, I'm talking any of the plants species you might have issues with, the finikyest plants you can think of............, then you'll know and see that this is not the same as CO2 in a liquid..........30ppm is fine and will not help by adding more, but that is for a liquid medium........

No one ever said anything nor tested it with gas+the liquid at 30ppm.

Given folk's complacency and CO2 related issues, amping the CO2 is a good thing and does not require that much effort or cost to do so.

We do not have to add so much PO4 either............but many do............

You can slow plant growth down the simplest way, use less light.

I have made some graphs and have 3 more test to complete on this issue, then I'll present it in the BarrReport this month.
8 folks have reported the same results as myself in terms of tank response.

Regards, 
Tom Barr

www.BarrReport.com


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## Happy Camper (Sep 13, 2005)

StUk_In_AfRiKa said:


> And I'm sorry if I'm confusing anyone with all this


Hello Stuck in Africa, I've seen you round the G4Y forums, nice to see you here. Do you have pics of your tank to share? I'd love to see.

Kind Regards
Cameron


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## jbaker6953 (Sep 18, 2005)

plantbrain said:


> 1.The initial few minutes/hour/s(typically 1 to 3 hours after the light/CO2 comes on) are mainly dissolving the CO2 into solution.
> 
> 2.Once a high level builds up, then it becomes much more difficult for the CO2 mist to be dissolved. Chemically: it is more difficult to dissolve a substance against an increasingly larger concentrational gradient.


According to ""The Solubility of Carbon Dioxide in Water at Low Pressure", _Journal of Physical and Chemical Reference Data_, 20, 1201-1209, (1991), CO2 isn't saturated until you approach 622 ppm at 25C.



plantbrain said:


> Now, what about the CO2 bubbles at 30ppm?
> 
> Are they so quick to dissolve at this level of CO2?


They should, it's only about 4.8% of saturation.



plantbrain said:


> You are adding CO2 to a solution that is already heavily super saturated.
> The O2 is at best only mildly super staurated.


The CO2 is nowhere near saturated. See above reference.



plantbrain said:


> After 1-2 hours, the micro bubbles will persist and float around the tank.
> This is true for my venturi reactors as well.
> That gas build up in the external reactor tubes as well as the internal venrturis are similar later in the day.Think about what that gas might be, I'd suggested it was O2 at one point, the flame test was not conclusive(it put the flame out, suggesting CO2, not O2).


The problem with using a flame test to determine the presence of O2 is that organic substances will not burn when the concentration of O2 is below around 16% at normal humidity levels. See "Burning of forest materials under late Paleozoic high atmospheric oxygen levels." So, you could have 15% O2 in the reactor tube and your flame test would lead you to conclude that it wasn't O2.



plantbrain said:


> So this means, and I know I'm right(rare), that the CO2 dissolving is greatly reduced later at a stable given CO2 dosing rate in the day after you build up to a certain level. What level? I'd guess about 30ppm.


Why not measure it instead of guessing? It will only take a second. 



plantbrain said:


> It is not one _or_ the other, they are synergistic, one complement and builds on the other.
> My mistake in the past was assuming that the gas in the tube was O2, it's not, it's CO2 excess that's much more difficult to dissolve.


This is speculation without testing and other data seems to contraindicate insoluble CO2.



plantbrain said:


> 30ppm bathes the entire plant, the mist of relatively pure CO2 bathes part of the plant.
> Together both drive photosynthesis at a rapid rate that I've observed.


It has been noted by Dave Huebert that photosynthesis in submerged macrophytes (aquatic plants) is saturated at 30ppm CO2. If that is the case, increasing availability of CO2 above and beyond saturation will have no effect. There are some experimental data that suggest increasing CO2 very much above saturation actually decreases O2 production ("Effects of CO2 concentration and light intensity on photosynthesis of a rootless submerged plant, Ceratophyllum demersum L... ", _Adv Space Res._ 2003;31(7):1743-9).


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## unirdna (Jan 22, 2004)

*This is still not convincing.*



plantbrain said:


> Dissolved versus undissolved bubbles.............this is where folks are getting boondoggled.
> There is a two step process.
> 
> 1.The initial few minutes/hour/s(typically 1 to 3 hours after the light/CO2 comes on) are mainly dissolving the CO2 into solution.
> ...



I don't think I'm getting boondoggled at all. Your data simply is not convincing. This is because CO2 solubility and O2 solubility are apples and oranges. O2 reaches saturation at around 12ppm (parts per million). CO2 saturation is significantly higher - much much much higher.

Graph from the pages of Dr. James Baird, Professor, Chemical Physics - Brown University









At 25C, saturation of CO2 is .15g/100ml water. That is 1500ppm! Your claim that CO2 is "already heavily supersaturated, while O2 is mildly supersaturated" is incorrect. CO2 is not supersaturated. O2, on the other hand, is frequenly saturated, and this is why plants pearl. Supersaturation is also achieved by reducing temp or increasing pressure (thus, increasing the solubility of O2), and then returning to the original conditions. O2 will then bubble out of solution because the solubility is decreased. This is why bubbles form on the walls of tanks when they are first set up with tap water. Tap water is under pressure (higher O2 solubility). It's also the reason that we frequently see pearling after a water change. The addition of supersaturated (O2) water can saturate or supersaturate that tank water with O2; thus, any/all O2 given off by the plants will not dissolve - creating the pearling effect.

Your claim that CO2 is more saturated than O2 is also incorrect. Again, I draw your attention to the solubilty graph of CO2. 30ppm out of the 1500ppm means that the "magic number" - 30ppm - for CO2 levels in planted aqaria is less than 1% of CO2 saturation. To claim that CO2 starts to become harder to dissolve at .2% saturation seems unlikely. Furthermore, there are many anecdotal instances of pH crashes, fish kills, etc. that add further speculation to the "harder to dissolve" idea.

On the other hand, we know that most fish species need at least 5ppm O2 to survive. And, since water becomes saturated with O2 at about 12 ppm, we would know that it would take a maximum 7ppm increase in O2 (for any tank) to create conditions where O2 would be saturated. And you say that in the AM when the lights come on, the tiny bubbles are not present. Yet later on, once the plants been photosynthesizing for a while, these bubbles become present. hmmm.





plantbrain said:


> After 1-2 hours, the micro bubbles will persist and float around the tank.
> This is true for my venturi reactors as well.
> That gas build up in the external reactor tubes as well as the internal venrturis are similar later in the day.Think about what that gas might be, I'd suggested it was O2 at one point, the flame test was not conclusive(it put the flame out, suggesting CO2, not O2).
> 
> ...



I'm starting to think you are putting too much stock in your "flame test" results. I question the methods in which your flame test was performed. You say that the gas put out the flame. You must have had a method in which you collected this gas, and then inserted a flame into an enclosed area with this gas. Is it possible that the flame quickly exhausted all the O2 and put itself out? Explain your methods.

As for your venturi reactors, what you have described is exactly what I would expect. First off, as we have seen, CO2 is NOT at supersaturation. The only gas that IS is O2. Thus the only gas eager to come out of solution would be O2. 

I think your venturi only helps to do one thing - get rid of O2 buildup. The O2 in continually chopped up into smaller bubbles that do not have enough buoyancy to fight the current, and are thus forced out the bottome of your reactor and escape to the surface. That buildup of gas is NOT CO2.



plantbrain said:


> So this means, and I know I'm right(rare), that the CO2 dissolving is greatly reduced later at a stable given CO2 dosing rate in the day after you build up to a certain level. What level? I'd guess about 30ppm.
> 
> After you get this into the tank( 30ppm dissolved CO2), then this CO2 micro bubble theory starts to work. You still have 30ppm in the tank, but now you have added pulse of pure CO2 mist on top of that for the plants.
> 
> ...


See about explanation for why the gas in the venturi is "dissolving". 

You have confused cause and effect because of a few minor confusions -your flame test, and your misunderstanding of CO2 solubility.





plantbrain said:


> I tried this without any plants(thus no O2 build up), I had gas build up later in the day, thus reduction in CO2 dissolving at higher ppm levels.


This is the only piece of compelling data I see. Yet, again, I draw your attention to the vast solubility differences between CO2 and O2. It wouldn't take much "impurity" O2 (from your CO2 system - eg. small line leaks, tank impurities, diffusion into tubing, etc) to saturated the water, thus allowing small bubbles of O2 to circulate in the tank.


To conclude. I want to reiterate that I do NOT question whether or not this "blowing diffusion" method helps plants grow. I do not doubt that good circulation of CO2 around a tank it a good thing. I know I see better growth near my spray bar than on the other side of the tank. But all your claims about CO2 solubility are wrong, and you steadfast conclusions need to be reexamined.

Ted


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## jbaker6953 (Sep 18, 2005)

unirdna said:


> At 25C, saturation of CO2 is .15g/100ml water. That is 1500ppm!


For those that might be confused because the paper I linked to suggests 622ppm and Henry's Law suggests 1500ppm, there is an explanation. The 622ppm was a figure meaning, "622 molecules of CO2 and 999,378 molecules of water." When we use the figure in our aquariums, we are using mg/L. The 622 figure works out to 1519 mg/L.

I feel compelled to point out that I took this data from the wrong table in the report, and the actual value is 0.000609 mole fractions - that is closer 1,488 mg/L for CO2 saturation at 25C.


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## jgc (Jul 6, 2005)

just to points.

1) if there is measurable increase in plant growth, something is happening. We may disagree why, but the first step is to duplicate the experiment. We have seen cold fusion claims here. But so far there appears to be people able to duplicate and we will get more comfimation tests over the next few weeks (either positive or negitive).

2) Lab and real world are two seperate places. Lab experiments for disolving c02 are probably using deionized water or distilled. We are using water with tons of impurities intentionally and unintentionally disolved in it, not to mention our water hits 02 saturation daily. How does the real world environment we grow stuff in change the lab results.
---
I have very little education in science. It was a hobby once upon a time. A hobby that managed to get me a fully scholarship back then, but was only persued via other hobbies since.


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## jbaker6953 (Sep 18, 2005)

jgc said:


> just to points.
> 
> 1) if there is measurable increase in plant growth, something is happening. We may disagree why, but the first step is to duplicate the experiment. We have seen cold fusion claims here. But so far there appears to be people able to duplicate and we will get more comfimation tests over the next few weeks (either positive or negitive).


We do not yet have enough data to make a determination about whether the reports of successful duplication are the result of increased CO2 availability. Did the reporters have equal circulation prior to beginning the experiment? What was the growth rate prior, and what is it now? Is it measured, or just eyeballed?



jgc said:


> 2) Lab and real world are two seperate places. Lab experiments for disolving c02 are probably using deionized water or distilled. We are using water with tons of impurities intentionally and unintentionally disolved in it, not to mention our water hits 02 saturation daily. How does the real world environment we grow stuff in change the lab results.


The lab and the real world are two different places, but luckily for us the laws of nature remain the same regardless of physical location. Water has the same density everywhere, and CO2 solubility is the same everywhere. The effect of dissolved solids even in hard freshwater (500 ppm) on the solubility of CO2 is negligible. Probably somewhere around 0.5% if I recall correctly.


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## lumpyfunk (Dec 22, 2004)

I have to agree with jgc, debating the validity of Tom Barr's theory with out testing it first is moot. What needs to be done it try it to see if it works and then figuring out why it worked or didnt. After all in 1492 scientific concensus was that the world was flat and if you sailed to far you would fall off the edge, we now know this is not the case but when Columbus set sail most people thought he was wrong.


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## unirdna (Jan 22, 2004)

lumpyfunk said:


> I have to agree with jgc, debating the validity of Tom Barr's theory with out testing it first is moot. What needs to be done it try it to see if it works and then figuring out why it worked or didnt. After all in 1492 scientific concensus was that the world was flat and if you sailed to far you would fall off the edge, we now know this is not the case but when Columbus set sail most people thought he was wrong.



Ladies and Gentlemen, please :icon_conf .

No one is debating the validity of a theory. Mr. Barr has elected to draw conclusions based on increased plant growth. His conclusions contest well-known chemical/physical KNOWNS. This is what we are debating. If he had simply said "I tried so-n-so, and got much more plant growth", I would never had taken opposition. But, he went on to state WHY this happens, and that is why we are debating.

Nice analogy, btw, lumpy. But Columbus was way off on his mercantile math since he opted to use Ptolemy's world estimate instead of Erathothonese (sp?). Had the "new" world not been "in his way", he would have killed himself and his crew. His discovery was purly by luck. His conclusions were wrong.


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## jbaker6953 (Sep 18, 2005)

lumpyfunk said:


> I have to agree with jgc, debating the validity of Tom Barr's theory with out testing it first is moot. What needs to be done it try it to see if it works and then figuring out why it worked or didnt. After all in 1492 scientific concensus was that the world was flat and if you sailed to far you would fall off the edge, we now know this is not the case but when Columbus set sail most people thought he was wrong.


There are some things about which we have _a priori_ knowledge. That is to say, we know whether it's correct or incorrect without further testing. For example, if someone claims that they have a perpetual motion machine, we know they are incorrect. We do not need to go out and build one according to their plans to see if it works. The point being that it is not always necessary to test a theory.

The scientific community was aware of the spherical nature of the Earth for a millenium before Columbus set sail. But, even so, the test of whether the Earth is flat or not is a binary one. It either is, or isn't. There are no variables to consider, nor extraneous conditions to affect the results. It just is, or isn't. A simple observation to confirm or deny a theory. No data are required to replicate the experiment.

Tom Barr's theory that creating a circulation of small bubbles from a CO2 diffuser increases the rate of photsynthesis is not a binary proposition. We do not know what the growth rate was before the experiment, nor after. The rate of photosynthesis or oxygen respiration prior to, and after, is not provided to us. We have no information about the amount or magnitude of the circulation employed before and after the experiment. We essentially have nothing except, "_put some bubbles under a spray bar to make them fly around the tank._" A valid scientific theory makes predictions that can be confirmed or disproved. They also are subject to the falsification principle. In other words, it has to be possible for some plausible set of conditions to prove the theory wrong. A theory that cannot make reliable predictions, and cannot be proven wrong under any circumstances, does not contribute to scientific knowledge.

Suppose we set out to conduct our own experiment to confirm or deny Tom's theory. What quantifiable predicitions does the theory make? What result would constitute a confirmation, and what result would mean a failure? Where is the dividing line between confirmation and a failure to confirm? We do not know because we have no hard data on the original experiment. There is no way to replicate the experiment without data on how the experiment was conducted, the control, and how the results were determined.

One of the theories as to why the bubbles are able to persist long enough to circulate and stick to plants was that CO2 is already saturated at 30 mg/L, thus preventing further dissolution. The data presented do not support that theory. 30 mg/L represents only 2.02% saturation at 25°C (77°F), and so we know that CO2 saturation is not likely to be the explanation for the persistence of the bubbles. Further examination of the contents of these bubbles is required. If their persistence is due to their composition being gases other than CO2, the entire theory collapses. That is why the strong focus on the compsition of these bubbles.

The veracity of the theory is also called into question by other data. It has been written that saturation of photosynthesis in aquatic plants occurs at around 30 mg/L. Saturation means that adding more CO2 will not result in more photosynthesis. There are also further studies that suggest photosynthesis in aquatic plants actually _decreases_ in the presence of higher levels of CO2. Both of these data points, in addition to the solubility of CO2, cast critical doubts on the theory that CO2 bubbles are driving increased photosynthesis in the plants.


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## jgc (Jul 6, 2005)

Here is mho, with no rational basis in science. Once co2 is dissolved into solution, the solution will probably have a fairly uniform dispersion of co2 (even if our pumps were not working much). I suspect concentration will be slightly higher at parts of the aquarium (like right downstream from the diffuser) than others - right after the huge plant in front of the filter return). But suspect that absorption of co2 by the plants is slow enough that the differences in dissolved co2 around the tank will be pretty much un-measurable.

That said - I suspect that localized high ppm concentrations may exist in the solution right next to the co2 bubbles (such as the ones stuck on leafs).

So that question goes to this. Is the ppm in the .01 ml of solution surrounding the bubble measurable different than the solution taken as a whole. I understand any localized difference would be rapidly diffusing through out the solution, but meanwhile co2 would also be diffusing into that surrounding solution as well.

Sometimes enjoy analogies. It might only be 10% humidity and 100 degrees out, but when you are standing under a mister, it feels differently to you.

I want to believe in cold fusion... Am most interested in seeing the experiment replicated and documented, then trying to find out why.


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## jbaker6953 (Sep 18, 2005)

jgc said:


> That said - I suspect that localized high ppm concentrations may exist in the solution right next to the co2 bubbles (such as the ones stuck on leafs).


That's the point about the 30 mg/L saturation point. If it's true that 30 mg/L is the saturation point for photosynthesis, it doesn't matter how much more there is next to the bubbles because additional photosynthesis will not happen. There is also a study that found that elevated CO2 levels actually decreased photosynthesis.



jgc said:


> Sometimes enjoy analogies. It might only be 10% humidity and 100 degrees out, but when you are standing under a mister, it feels differently to you.


In this case, the analogy would be like asking if it will feel different to you when you are underwater when it's raining, or when it's clear.


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## Blue (May 29, 2005)

I don't see why these posts should be allowed here, which are obviously "nicely worded" attacks on Tom Barr, a person who has helped hundreds (if not thousands) of people achieve beautiful planted tanks.

The only point they are addressing in their lengthy and thinly veiled attacks is the fact that Tom may have made an error in using the term "CO2 saturation." Perhaps the CO2 levels are NOT "saturated," but do these posters know if CO2 bubbles form more easily and stick around longer if the levels are at 30 ppm as opposed to 0 ppm? Of course not... but they attempt to trick you into thinking they are discrediting Tom Barr by citing works that are hardly relevant to Mr. Barr's original points.

And Mr. Barr's original point still stands. Diffusers blowing small/micro bubbles over the tank yields better results than using a CO2 reactor that dissolves CO2 only w/ little to no bubbles. Hypancistrus noted that Amano tanks (which few can argue are nothing short of breathtaking) uses diffusers on the OPPOSITE end as the flow for smaller tanks and diffusers on the SAME end as the flow for larger tanks (despite some obviously jealous people flaming him for posting pics of Amano tanks).


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## stcyrwm (Sep 1, 2005)

jbaker6953 said:


> For those that might be confused because the paper I linked to suggests 622ppm and Henry's Law suggests 1500ppm, there is an explanation. The 622ppm was a figure meaning, "622 molecules of CO2 and 999,378 molecules of water." When we use the figure in our aquariums, we are using mg/L. The 622 figure works out to 1519 mg/L.
> 
> I feel compelled to point out that I took this data from the wrong table in the report, and the actual value is 0.000609 mole fractions - that is closer 1,488 mg/L for CO2 saturation at 25C.


That clears everything up :icon_wink


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## unirdna (Jan 22, 2004)

stcyrwm said:


> That clears everything up :icon_wink


http://wine1.sb.fsu.edu/chm1045/tables/period/PT_large.jpg

Atomic weight of water = 18 (2 Hydrogen @ 1 a piece, and one Oxygen @ 16)
Atomic weight of Carbon Dioxide = 44 (1 Carbon @ 12, and two Oxygen @ 16)

(622 molecules CO2 (per approximately one million molecules H20) * atomic weight CO2) / atomic weight H2O

(622 * 44) / 18 = 1522 PARTS per million CO2 (since it is a larger molecule)

 back at ya

----------------------------------------------------------------------

Back to the discussion. Tom?


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## Rex Grigg (Dec 10, 2002)

I personally am getting a huge kick out of this thread. I don't see it as attacks.

If someone, anyone, wants to come in and make statements or claims then they should be prepared to back them up. All to often people come to this forum and make claims about things. When questioned they either leave, clam up, or lie.

This is nothing but a very civil scientific debate.


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## shalu (Jan 16, 2003)

Blue said:


> The only point they are addressing in their lengthy and thinly veiled attacks is the fact that Tom may have made an error in using the term "CO2 saturation." Perhaps the CO2 levels are NOT "saturated," but do these posters know if CO2 bubbles form more easily and stick around longer if the levels are at 30 ppm as opposed to 0 ppm? Of course not... but they attempt to trick you into thinking they are discrediting Tom Barr by citing works that are hardly relevant to Mr. Barr's original points.


Good point.


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## scolley (Apr 4, 2004)

Rex Grigg said:


> I personally am getting a huge kick out of this thread. I don't see it as attacks.
> 
> If someone, anyone, wants to come in and make statements or claims then they should be prepared to back them up. All to often people come to this forum and make claims about things. When questioned they either leave, clam up, or lie.
> 
> This is nothing but a very civil scientific debate.


Strongly agreed. There is absolutely nothing wrong with coming to this forum and stating opinion. We all learn from that - especially when hard facts are not available.

But if you are stating something as fact, your ability to back that up is how we validate the information - another way the whole community learns.

I don't see attacks here. I see peoples' genuine desire to separate the information wheat from the chaff.


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## jbaker6953 (Sep 18, 2005)

Blue said:


> The only point they are addressing in their lengthy and thinly veiled attacks is the fact that Tom may have made an error in using the term "CO2 saturation." Perhaps the CO2 levels are NOT "saturated," but do these posters know if CO2 bubbles form more easily and stick around longer if the levels are at 30 ppm as opposed to 0 ppm? Of course not... but they attempt to trick you into thinking they are discrediting Tom Barr by citing works that are hardly relevant to Mr. Barr's original points.


Tom's theory rests on the theory that carbon dioxide is saturated, or becomes significantly more difficult to dissolve, in the aquarium water once levels reach 30 mg/L. If that is not the case, then the theory is significantly weakened. That's not an attack, and it's not personal.

I can hardly think of anything more relevant to the saturation level of carbon dioxide in water than a study entitled, "The Solubility of Carbon Dioxide in Water at Low Pressure." Can you? According to that study, we should expect to see saturation at 1488 mg/L in plain old water at 77F under normal atmospheric pressure. You can't get more relevant than that.

Not only is 30 mg/L nowhere near saturation, but 30 mg/L has virtually no effect on the diffusion rate of CO2. Fick's Law has that diffusion is governed by the diffusion coefficient, surface area, concentration gradient, and the thickness of the diffusion barrier. In the case of bubbling CO2 in water, everything remains constant except for the concentration gradient. In that case, we start out with a huge gradient (pure CO2 to nearly none in the water). As Tom stated, later on the concentration gradient has only changed by 0.003% - from nearly 1,000,000 ppm to 999,970 ppm difference. That should have a proportional effect on the rate of diffusion.

That means that the bubbles are not persisting because CO2 is saturated, or more difficult to dissolve at 30 mg/L. The data contradicts the theory. That's not an attack. Since the persistence of the bubbles is not due to CO2 solubility, there is something else going on. One likely possibility is that the bubbles are not CO2, but instead composed of impurities from the CO2 tank and gases that have diffused into the bubble. Think of it as the bubble swapping CO2 for other gases in the water as it travels around the tank.



Blue said:


> And Mr. Barr's original point still stands. Diffusers blowing small/micro bubbles over the tank yields better results than using a CO2 reactor that dissolves CO2 only w/ little to no bubbles.


That may be the case. I don't think anyone is questioning whether Tom saw better growth after changing his setup. I don't believe Tom would lie to us about seeing better growth. I think what is being called into question is the cause of the better growth and pearling. It does not appear that the data support the theory that CO2 availability is increased by attaching bubbles of nearly pure CO2 to the plant leaves.



Blue said:


> Hypancistrus noted that Amano tanks (which few can argue are nothing short of breathtaking) uses diffusers on the OPPOSITE end as the flow for smaller tanks and diffusers on the SAME end as the flow for larger tanks (despite some obviously jealous people flaming him for posting pics of Amano tanks).


I'm not sure what this has to do with the rest of the post.


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## windsurfer (Mar 8, 2005)

While I have no opinion on the efficacy of using CO2 mist to grow plants, I do have some observations about the bubbles in my CO2 injector.

I inject CO2 24/7 via a vortex diffuser driven by a powerhead. Gas is run open loop using a regulator and a needle valve only, no pH controller. In one of the tanks, my pH is 6.9 at lights on and the CO2 diffuser is dead quiet. By afternoon the pH goes up to 7.0 (30ppm), the plants begin to pearl lightly, and the diffuser begins to gurgle due to the presence of a bubble. This time of year I am getting about 45min of direct sun on this tank in the evening. At the end of this period, the plants are pearling massively and the diffuser gurgling loudly. pH is 7.1

If the bubble in the diffuser were undissolved CO2, the worst case would be in the morning just before the lights come on when CO2 in the tank is at its highest. But at that time the diffuser is silent with no bubble. It is not until the O2 content of the water begins to approach saturation and the plants start pearling that the diffuser gets a bubble and begins to gurgle. This supports the hypothesis that the gas is indeed a result of high O2 levels and not the CO2 becoming saturated.

Why would I collect O2 in the diffuser which is pressurized relative to the tank ? One possibility is cavitation by the highly inefficient powerhead impeller. In this case the pressure immediately behind the impeller vanes may be low enough to cause some of the dissolved oxygen to come out of solution. These bubbles would then be blown into the diffuser, where the reduction in pressure would inflate them allowing them to agglomerate into a larger bubble and cause the gurgling sound.

One possible way to test what the gas in the diffuser is to use the enormous difference in reactivity between CO2 and O2. O2 is a aggressive oxidizer while CO2 is quite inert. You could take something like a pair of brass washers, etch them to an equal starting point using HNO3, and place one in the diffuser where the bubble forms. The other can be mounted in the tank just outside the diffuser to serve as a control. Both washers can then be removed periodically to inspect for oxidation. If the gas in the diffuser were CO2, the brass in the reactor will change no more quickly than the brass in the water outside the reactor. If the gas in the reactor is O2, it will rapidly oxidize the brass and the patina quite quickly become noticeably darker than the control located outside the reactor.

-jd


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## jbaker6953 (Sep 18, 2005)

windsurfer said:


> One possible way to test what the gas in the diffuser is to use the enormous difference in reactivity between CO2 and O2.


I might have a better way. Try leaving the lights off one day and see if the gas still builds up. If it doesn't, that would be pretty conclusive proof that the gas is not CO2. If it builds up even with the lights off it probably is CO2. I wouldn't worry about the fish, but you might do it on a weekend when you can watch the tank periodically to make sure nothing bad is happening.


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## SCMurphy (Oct 21, 2003)

The gas bubble in the reactor is probably the result of O2 supersaturation. Is it O2, not necessarily. When O2 becomes supersaturated it can force N2 out of the water, partial pressures of gasses that don't dissociate are interrelated. The more O2 in solution the less N2 there can be in solution at atmospheric pressure. Would the gas in the reactor put out a flame if it were N2? Yes. 

I'm really enjoying this debate. I wouldn't be surprised if it is just that the dispersion of dissolved CO2 is better and the across tank gradient of dissolved CO2 in ppm becomes more uniform when the micro bubbles are put into a current.


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## windsurfer (Mar 8, 2005)

"I wouldn't be surprised if it is just that the dispersion of dissolved CO2 is better and the across tank gradient of dissolved CO2 in ppm becomes more uniform when the micro bubbles are put into a current."

It could also be that the bubbles do a better job of getting the CO2 thru the boundry layer surrounding the plant leaves.

this boundry layer is certainly O2 rich -which is why the plants pearl before that DO in the tank reaches saturation, and very likely CO2 poor.

-jd


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## SCMurphy (Oct 21, 2003)

windsurfer said:


> It could also be that the bubbles do a better job of getting the CO2 thru the boundary layer surrounding the plant leaves.
> 
> this boundary layer is certainly O2 rich -which is why the plants pearl before that DO in the tank reaches saturation, and very likely CO2 poor.
> 
> -jd


Except it isn't likely that there is any appreciable CO2 left in the micro-bubbles when they reach a plant leaf on the other side of the tank. The whole reason to use a micro-bubble diffuser is to speed up the dissolution of CO2.


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## windsurfer (Mar 8, 2005)

"Except it isn't likely that there is any appreciable CO2 left in the micro-bubbles when they reach a plant leaf on the other side of the tank. The whole reason to use a micro-bubble diffuser is to speed up the dissolution of CO2."

it may not matter if there is plenty of CO2 in the water outside the boundry layer. The bubble can act as a mixer stirring the boundry layer and promoting CO2 diffusion from the surrounding water to the leaf.

-jd


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## jbaker6953 (Sep 18, 2005)

windsurfer said:


> It could also be that the bubbles do a better job of getting the CO2 thru the boundry layer surrounding the plant leaves.


 That is the center of this entire debate. Myself and some others do not think it is likely that these bubbles even contain significant amounts of CO2 by the time they stick to a leaf. Even if they were still CO2, there is further evidence that photosynthesis is already saturated at 30 mg/L. If that is the case adding more CO2 by penetrating the Prandtl Boundary with a bubble won't do anything to increase photosynthesis. Not only will it not do anything, but it appears that levels of CO2 availability above a certain level will decrease photosynthesis.

In summary;

1) It is doubtful that the bubbles are CO2 because their persistence increases with time - a time when O2 saturation is achieved, but CO2 saturation is not. Since O2 saturation is reached, it becomes very likely that O2 is trying to "escape" by diffusing into the CO2 bubbles as they CO2 is diffusing out. The CO2 has no reason to stay because the water is nowhere near saturated with CO2.

2) Even if the bubbles were CO2, it is unlikely that they are driving increased photosynthesis simply because it appears that photosynthesis is already saturated with CO2 - it cannot use any more.

3) Another reason to doubt that bubbles of CO2 attaching to the leaves are increasing photosynthesis is the fact that high levels of CO2 have been shown to decrease photosynthesis, not increase it.


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## unirdna (Jan 22, 2004)

SCMurphy said:


> The gas bubble in the reactor is probably the result of O2 supersaturation. Is it O2, not necessarily. When O2 becomes supersaturated it can force N2 out of the water, partial pressures of gasses that don't dissociate are interrelated. The more O2 in solution the less N2 there can be in solution at atmospheric pressure. Would the gas in the reactor put out a flame if it were N2? Yes.





unirdna said:


> First off, as we have seen, CO2 is NOT at supersaturation. The only gas that IS is O2. Thus the only gas eager to come out of solution would be O2


Sean, I know that Nitrogen gas equilibrium is around 15-20ppm in water (with aquaria temps). Basically twice as much as O2. Everything you've said about non-dissociating gasses is consistent with what I've learned, but I did not know that N2 can be _forced_ out of solution due to oxygen (super)saturation. I'd like to read more about this. Do you have any sources?

If this is a fact, then I think we have a whole new dimension to this debate roud:


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## windsurfer (Mar 8, 2005)

“there is further evidence that photosynthesis is already saturated at 30 mg/L. If that is the case adding more CO2 by penetrating the Prandtl Boundary with a bubble won't do anything to increase photosynthesis”

30ppm measured where ? I don’t have ready access to the reference listed and the link supplied only gave the abstract which included:

“The water in the vessel was aerated sufficiently with a gas containing a known concentration of CO2 gas mixed with N2 gas before closing the vessel. The CO2 concentrations in the aerating gas ranged from 0.3 to 10 mmol mol-1.”

I laughed when I saw they were adding CO2 by bubbling it thru the solution…

If the plant is photosynthesizing strongly (consuming CO2), the water in the boundary layer will have less CO2 than the surrounding water. If the photosynthesis is limited by CO2 (i.e. below saturation), the limiting factor may be the rate of CO2 diffusion thru the boundary layer. If this is the case, doing something that increases CO2 diffusion would increase the photosynthesis rate. Things that could do this include: Stirring via bubbles, thinning via increased current, stirring via agitation of the plant, addition of vortex generators to energize the boundary layer, increasing the concentration on CO2 in the surrounding water, etc.

-jd


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## jbaker6953 (Sep 18, 2005)

windsurfer said:


> 30ppm measured where ? I don’t have ready access to the reference listed and the link supplied only gave the abstract


That's the paper about how high levels of CO2 inhibit, rather than promote, photosynthesis. The article about 30 mg/L saturating photosynthesis is by Dave Huebert and is at aquabotanic.com. The article is talking about 30 mg/L in the water column.



windsurfer said:


> I laughed when I saw they were adding CO2 by bubbling it thru the solution…


 Do you add it in a different manner?


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## SCMurphy (Oct 21, 2003)

I don't have a source just a pair of physics law to lean on.

Dalton's law of partial pressures.
The total pressure of a mixture of gases equals the sum of the pressures that each would exert if it were present alone.

Henry's law
The concentration of a solute gas in a solution is directly proportional to the partial pressure of that gas above the solution.

N2 and O2 do not really dissolve, they go into solution because of atmospheric pressure, in fact they go into solution based on the amount of pressure they each cause.

We did an experiment in my Ichthyology class, college was a few years ago, which was the reverse of this. We bubbled N2 into a covered 10 gallon aquarium holding 3 or 4 small fish and timed the 'reaction', the increased respiration in response to the reduced O2. The reaction was very fast, much faster than could be achieved by the fish simply using up the O2 available in solution. 

So, increasing the partial pressure of the O2 causes a decrease in the partial pressure of the N2 because the total pressure remained constant. N2 has to leave solution.


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## windsurfer (Mar 8, 2005)

“The article about 30 mg/L saturating photosynthesis is by Dave Huebert and is at aquabotanic.com. The article is talking about 30 mg/L in the water column.”

if it is this article:
Water Plants 101
A basic introduction to the physiology and ecology of aquatic plants
by Dave Huebert

Located at: http://www.aquabotanic.com/wp101.htm

The first comment is this is not a refereed journal, so not knowing the author I have no way to judge it’s scientific validity. Having said that, it does appear to be a relatively well written primer. The only comment on CO2 saturation I saw in the article is:

“CO2 diffuses about ten thousand times slower in water than in air. This problem is compounded by the relatively thick unstirred layer (or Prandtl boundary) that surrounds aquatic plant leaves. The unstirred layer in aquatic plants is a layer of still water through which gases and nutrients must diffuse to reach the plant leaf. It is about 0.5 mm thick, which is ten times thicker than in terrestrial plants. The result is that approximately 30 mg/L free CO2 is required to saturate photosynthesis in submerged aquatic plants.”


My comment about this is that if the CO2 is measured in the bulk water column, the CO2 in the boundry layer (available to the plant) can vary dramatically depending on many factors including photosynthesis rate (CO2 consumptin), current, agitation (stirring), etc. Thus I would take this to be a case of “this is what I measured in my situation” and not a universal truth than could be applied to all situations to all plants.

-jd


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## jbaker6953 (Sep 18, 2005)

SCMurphy said:


> So, increasing the partial pressure of the O2 causes a decrease in the partial pressure of the N2 because the total pressure remained constant. N2 has to leave solution.


At first I was going to reply that this doesn't make sense since adding CO2 doesn't drive out other gases, but the more I thought about it, the more it did make sense. CO2 doesn't drive O2 or N2 out because of its peculiar property of forming various carbonates when dissolved in water. This allows it to exist without driving up the total pressure of the dissolved gases as much as if it all remained as CO2 in solution. That's why it takes 1500 mg/L to saturate water with CO2, but only 12 mg/L for O2. That's pretty counterintuitive considering that CO2 is 50% more massive than O2. But, for N2 or O2, as soon as one is added the other is driven out by necessity of keeping the total pressure constant. It fits. I like it.


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## jbaker6953 (Sep 18, 2005)

windsurfer said:


> The first comment is this is not a refereed journal, so not knowing the author I have no way to judge it’s scientific validity.


I have my reservations about that as well. I am still looking for a refereed article dealing with this. Please look too. Two sets of eyes are better than one.


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## baj (Sep 16, 2004)

umm sidetrack here, why does stirring the water dissolve oxygen but displace carbon-di-oxide?


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## SCMurphy (Oct 21, 2003)

baj said:


> umm sidetrack here, why does stirring the water dissolve oxygen but displace carbon-di-oxide?


This belongs in a seperate thread. 

It has to do with the two Physics laws I mentioned before.

In a plantless tank O2 is consumed and CO2 is produced, both processes result in changes in the equilibrium with the partial pressures of these gases in the atmosphere. When you 'stir' the water so that the surface is disturbed what you are doing is speeding up the rebalancing of the gas concentrations by artificially increasing the surface area of the tank. O2 is low so more enters the solution, CO2 is high so some degasses. 

In a planted tank when O2 is at saturation levels you can’t increase O2 by stirring, only decrease it, the same as in nature except in rare instances at the base of tall dams. Since we are pumping CO2 into our tanks it can reach partial pressure levels that are higher than the atmosphere levels, so stirring the surface will degas both O2 and CO2.

If you have a planted tank that is not being injected with CO2, stir the surface to at least get some from the atmosphere.


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## windsurfer (Mar 8, 2005)

Um, I was referring to the boundary layer surrounding the plant leaves, not the water surface. The description in the aquabotanic article has a reasonable description and I’ll try to add to it a little.

In our aquariums, we have a situation with relatively small geometries (plant leaves) and relatively low velocities (current). In this situation, the flow of water around things (plant) is laminar (smooth). At low Reynolds numbers (low speeds, small geometries) laminar flow is accompanied by s relatively thick stagnant layer surrounding the objects (plants). Thickness of this layer is in the range of .25 to 1mm for our situation. Since the diffusitivities are limited, the concentration of dissolved gasses can be significantly different in these stagnant areas than in the surrounding water. Thus what you measure in your aquarium with a non-reactive probe (DO, ORP, pH) is not necessarily the same as what the plant experiences in the water immediately surrounding it. The most obvious example for me is the facts that plants will pearl when the total dissolved oxygen in the tank is below saturation. Huh ? when a plant pearls, it is because the oxygen level is above the saturation level and no more O2 can go into solution: thus it is released as a gas. How is this possible when a DO measurement shows the O2 is not saturated ? It is because the DO in the boundary layer is saturated, and the gas is being evolved out of the plant faster than it can be diffused out of the boundary layer. The same effect could be happening with CO2, the plant could be removing CO2 from the boundary layer faster than CO2 can be diffused into the boundary layer.

If this is the case, we can increase CO2 available to the plant by doing something that mixes (stirs) the boundary layer water with the surrounding water. Increasing circulation (velocity) can improve diffusion rates by making the boundary layer thinner. Things that add turbulence to the flow are even better –irregular leaf outlines may do this, bubbles may do this, and that is what the little fence thingys on airplane wings are doing: adding turbulence to the flow to disturb/thin the boundary layer.

My question to the botanists (like the one that started this thread PLANTBRAIN) is what is the effect of increased CO2 on plant growth, is there a saturation level ? if so what is it ? if terrestrial plants benefit from a very CO2 rich environment, why would aquatic plants be different ? What are the dynamics of CO2 use, is Co2 being used at the same rate as O2 is being generated?

I think we have heard enough from us physicists for now, it is time to hear from the botanists again…

-jd


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## scolley (Apr 4, 2004)

Thanks JD. That was a great explanation! roud:


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## SCMurphy (Oct 21, 2003)

JD, 

The surface stirring discussion wasn't in response to you, even if it does apply to the discussion. That was for someone else's benefit. 

Yep there is a boundary layer around plants leaves, yep it inhibits the transfer of CO2, yep it can be overcome by current. Yep plants overcome the boundary layer in many ways, thinner leaves, little or no cuticle, pinnate leaf structure, glabrous leaf surfaces, etc. But, if we are discussing overcoming the boundary layer and bubbles (or current) being the 'mixer' then we are discussing the uptake of aquious CO2, not gaseous.


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## windsurfer (Mar 8, 2005)

What I am throwing out there is that maybe the reason Tom’s plants seem to be growing faster with mist is because the bubbles are stirring the boundary layer and making the aqueous CO2 more available to the plant.

Perhaps he would see a similar response if he dissolved CO2 in a more conventional way and misted something inert like argon into the tank.

Maybe the reason his pH went up is because the plants absorbed it at a much higher rate than before, which is why they appear to him to be pearling better.

As previously stated by others, it is likely the persistent bubbles aren’t CO2 anyway. If they were, they would readily go into solution.

This is wild speculation. I know physics, not botany.

-jd


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## plantbrain (Dec 15, 2003)

SCMurphy said:


> JD,
> 
> The surface stirring discussion wasn't in response to you, even if it does apply to the discussion. That was for someone else's benefit.
> 
> Yep there is a boundary layer around plants leaves, yep it inhibits the transfer of CO2, yep it can be overcome by current. Yep plants overcome the boundary layer in many ways, thinner leaves, little or no cuticle, pinnate leaf structure, glabrous leaf surfaces, etc. But, if we are discussing overcoming the boundary layer and bubbles (or current) being the 'mixer' then we are discussing the uptake of aquious CO2, not gaseous.


Even in the gas form, and in us as well, the boundary layer is still there, but it's highly reduced with the gas.

the CO2 we expel goes across from a liquid to the gas form in our lungs acoss a liquid layer.

Look at Fick's law of diffusion.

Look at each symbol and what it means and think about it in terms of plant growth and mist etc.

Are the coefficients the same for a gas as they are for a liquid?
Nope.................

Regards, 
Tom Barr

www.BarrReport.com


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## plantbrain (Dec 15, 2003)

SCMurphy said:


> Except it isn't likely that there is any appreciable CO2 left in the micro-bubbles when they reach a plant leaf on the other side of the tank. The whole reason to use a micro-bubble diffuser is to speed up the dissolution of CO2.


Are you sure about that?

Do the micro bubbles instaneously dissolve as soon as they leave the disc?
No..............it takes a few seconds..............

Add more CO2 in solution, this also adds more time before the bubbles dissolve. Add current and this effectively blast the mist all over the weeds.

2-5 seconds vs 10-30 seconds is the time frame.
Yep, they dissolve, but at what __rate__?

I'd say it is likely there is a substantial amount of CO2 in the bubbles.
Given the souce of CO2 is 99.97% pure according to the supplies, what other gases are going to dissolve into a bubble in that time frame?

That is even more unlikely...............
Adding to that are the increases in O2 levels which is a direct function of plant growth.....................

And you can see the difference in the tank as well which is the meat and taters of this for hobbyists.

Anway, I have some test I'm doing the next week and will present them in the BarrReport that will show more on this issue.

Regards, 
Tom Barr 

www.BarrReport.com


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## lumpyfunk (Dec 22, 2004)

Is there a test that can be done to determine how long the micro bubles persist in a solution? Anyone got 10' of clear tubing we can try it with? lol


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## plantbrain (Dec 15, 2003)

jbaker6953 said:


> Tom Barr's theory that creating a circulation of small bubbles from a CO2 diffuser increases the rate of photsynthesis is not a binary proposition. We do not know what the growth rate was before the experiment, nor after. The rate of photosynthesis or oxygen respiration prior to, and after, is not provided to us.


No, but I have the data.......
And it is a significant increase in DO levels which is the standard for aquatic primary production.........



> Suppose we set out to conduct our own experiment to confirm or deny Tom's theory.


Now you are talking.



> What quantifiable predicitions does the theory make? What result would constitute a confirmation, and what result would mean a failure? Where is the dividing line between confirmation and a failure to confirm? We do not know because we have no hard data on the original experiment. There is no way to replicate the experiment without data on how the experiment was conducted, the control, and how the results were determined.


Yea there is, O2 levels.
There are a few other things as well that can be done.



> The data presented do not support that theory.
> 
> 
> > The data is for dissolved CO2, not gas.
> ...


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## SCMurphy (Oct 21, 2003)

plantbrain said:


> Are you sure about that?
> 
> Do the micro bubbles instaneously dissolve as soon as they leave the disc?
> No..............it takes a few seconds..............


Yes, I'm sure. The micro-bubble exists but it's not CO2 anymore.


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## plantbrain (Dec 15, 2003)

So what is the gas then and why do many folks have gas bubbles that disappear completely before hitting the surface?

Are some bubbles pure CO2 and some are not?

You cannot have it both ways.........

If these bubbles that are not CO2 build up and are more difficult to dissolve, why do they dissolved rapidly early in the morning?

O2 and CO2 are the two choices here as there are few other gases produced above saturation with air in our tanks. 

I have O2 tank and am adding it to a reactor to see as well as in the tank to artifically bump up the O2 levels to end of day levels.



Regards, 
Tom Barr


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## SCMurphy (Oct 21, 2003)

plantbrain said:


> So what is the gas then and why do many folks have gas bubbles that disappear completely before hitting the surface?
> 
> Are some bubbles pure CO2 and some are not?
> 
> You cannot have it both ways.........


Yes I can, basic aquatic physics.

They start as CO2, but within a few inches they aren't CO2 anymore. The CO2 has dissolved and partial pressure laws have set in and the bubbles are a combination of N2 and O2.


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## jgc (Jul 6, 2005)

Rex, forgive me these questions. Are you running co2 24/7? I am a little currious about your co2 levels thoughout the day. If you are not running co2 at night, you will be outgassing some and the plants will be usings some of the disolved 02. If you are running c02 at night, co2 levels in the morning will be at their highest rather than lowest.

Guess a quick experiment (if it does not kill fish) would be to see if you get the same micro bubble observation on tanks with and without night time c02 ingection.

Anyway, just a thought. I am still suspicious of this instantious co2 absorption theory - my ladder says differently. We would not be using diffusers and reactors if co2 would magically abosorb in micro seconds.


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## unirdna (Jan 22, 2004)

jgc said:


> If you are not running co2 at night, you will be outgassing some and the plants will be usings some of the disolved 02.
> 
> I am still suspicious of this instantious co2 absorption theory - my ladder says differently. We would not be using diffusers and reactors if co2 would magically abosorb in micro seconds.


jdc, please descibe what your ladder say and how you interpret the information.

And there is no magic involved. The speed/rate at which CO2 dissolves (like all other things that dissolve) is a function of the surface area to volume ratio. This makes sense for anyone who has ever eaten a piece of hard candy. Does is last longer if you suck on it, or bite it? Ahh, but why is it so satisfying to bite into the candy? Because it increased the surface to volume ratio and thus dissolves more quickly (in your saliva) and thus you get a burst of flavor. There are countless examples of this. I'm sure you can think of many.

So when we break CO2 into tiny bubbles via a diffuser, we are greatly increasing the surface area to volume ratio of the CO2 bubble. In simple terms, we have put more of the CO2 gas in contact with water.

If you don't have a diffuser, a bubble of CO2 would be large. Bubbling large CO2 into aquaria would be wasteful because as quickly and easily as CO2 does dissolve, a large bubble still will not dissolve completely if simply bubbled into the water. There are two reasons for this. 1. The amount of gas NOT in contact with water is many times higher (remember we need the gas and water to touch in order to dissolve). 2. The bubble doesn't spend nearly enough time in the water because, being large, it is way more buoyant, and so rises very quickly, limiting its contact time as well. Still, even if we were to simply bubble CO2 with no diffuser, you would still get CO2 into your water. If you didn't mind bubbling a few times as much CO2 as with a diffuser or reactor, you could certainly keep your tank at a optimal CO2 level. 

With reactors, we opt out of increasing surface area to volume, and use countercurrent (bubbles rise, water flows down) and (more) time to dissolve a "large" bubble (in seconds). 

Diffusers and reactors are designed to keep from wasting CO2, but this is not to say you can't get it into your water by simply bubbling CO2 through an airline hose. 


---------------------------------------------------------------

...all the confusion is due to folks not understanding how partial pressure governs gasses.

When you do not see a bubble of CO2 completely disappear, you assume that all the CO2 has not dissolved. This is wrong.

When your tank becomes saturated with O2 (at 10-12 ppm) because of photosynthesis, the O2 wants to escape the water. The O2 concentration in the water is higher than the equilibrium with the atmosphere, so it wants to escape back to the atmosphere.

But, lets think about this more critically. Henry's Law States "When a gas is in contact with the surface of a liquid, the amount of the gas which will go into solution is proportional to the partial pressure of that gas." The atmosphere is about 20% O2. Henry's Law says that when O2 is at 10ppm in water, any more O2 that is dissolved (given off by plants - photosynthesis) will want to escape to an atmosphere that already contains 20% O2.

Our bubbles of CO2 are almost pure CO2 (the debate goes on). The point is that there is little to no O2 in those bubbles when they first enter the water. So, the parital pressure of O2 in even lower in those bubbles than in the atmosphere. O2 not only will diffuse into those CO2 bubbles (while CO2 diffuses into the water), it actually prefers it!

So as O2 goes in and CO2 comes out, all the hobbiest sees is a stubborn bubble, refusing to dissolve.


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## jbaker6953 (Sep 18, 2005)

windsurfer said:


> Um, I was referring to the boundary layer surrounding the plant leaves, not the water surface. The description in the aquabotanic article has a reasonable description and I’ll try to add to it a little.


That's the reason that you have to elevate CO2 to 30 mg/L instead of the natural equillibirum. That figure has already taken into account the Prandtl Boundary. You need the 30 mg/L to drive diffusion across the boundary and into the plant at a rate that saturates photosynthesis. The whole idea of saturation is that adding more CO2, whether by increased concentration or increased availability, will do nothing to increase photosynthesis.


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## jbaker6953 (Sep 18, 2005)

plantbrain said:


> Are you sure about that?
> 
> Do the micro bubbles instaneously dissolve as soon as they leave the disc?
> No..............it takes a few seconds..............
> ...


That's the whole point. It doesn't take longer for CO2 to dissolve in a 30 mg/L solution than it does in a 0 mg/L solution. The difference according to Fick's Law is less than one or two percent. Even if we assume a full 2% difference, a bubble that took 3 seconds in the morning will take 3.06 seconds later in the day.


plantbrain said:


> I'd say it is likely there is a substantial amount of CO2 in the bubbles.
> Given the souce of CO2 is 99.97% pure according to the supplies, what other gases are going to dissolve into a bubble in that time frame?


O2 and N2. Once photosynthesis has saturated the water column with O2, these gases will be desperate to "get out."


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## windsurfer (Mar 8, 2005)

“That's the reason that you have to elevate CO2 to 30 mg/L instead of the natural equillibirum. That figure has already taken into account the Prandtl Boundary. You need the 30 mg/L to drive diffusion across the boundary and into the plant at a rate that saturates photosynthesis. The whole idea of saturation is that adding more CO2, whether by increased concentration or increased availability, will do nothing to increase photosynthesis.“



I have a very hard time getting that one by my personal BS filter…

1)	There has been no evidence presented here that Photosynthesis is saturated at 30ppm CO2. Plantbrain’s anecdotal evidence says he is still getting gains at 45-50-100ppm. That claim is at least as well supported as the one in the aquabotanic article cited earlier.

2)	There is no way a single number for saturation level could account for the boundary layer. There are just too many variables: flow, consumption rate, geometry, turbulence…

Unirdna makes a very good point…O2 and N2 definitely are diffusing into the bubble as CO2 is diffusing out. The CO2 is highly soluble in the water up to levels way beyond what our fish can tolerate, but as the DO levels rise, the rate of diffusion of O2 and N2 out of the water will increase.

-jd


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## jbaker6953 (Sep 18, 2005)

windsurfer said:


> I have a very hard time getting that one by my personal BS filter…
> 
> 1)	There has been no evidence presented here that Photosynthesis is saturated at 30ppm CO2. Plantbrain’s anecdotal evidence says he is still getting gains at 45-50-100ppm. That claim is at least as well supported as the one in the aquabotanic article cited earlier.


Are you referencing the article that states that photosynthesis in aquatic plants is saturated at 30 ppm?



windsurfer said:


> 2)	There is no way a single number for saturation level could account for the boundary layer. There are just too many variables: flow, consumption rate, geometry, turbulence…


Sure it could. That could be the upper limit under conditions of near absolute stillness. Increasing circulation would only decrease the CO2 needed to saturate photosynthesis.


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## windsurfer (Mar 8, 2005)

“Are you referencing the article that states that photosynthesis in aquatic plants is saturated at 30 ppm?”

yes, I am. That link is a very nice, but non-scientific, white paper that includes the statement “approximately 30 mg/L free CO2 is required to saturate photosynthesis in submerged aquatic plants” with no supporting evidence.

“Sure it could. That could be the upper limit under conditions of near absolute stillness. Increasing circulation would only decrease the CO2 needed to saturate photosynthesis”

Under conditions of absolute stillness, the amount of CO2 needed to saturate photosynthesis would be dependant on the amount of light. Also quite likely dependant on the species of plant.

-jd


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## unirdna (Jan 22, 2004)

windsurfer said:


> There is no way a single number for saturation level could account for the boundary layer. There are just too many variables: flow, consumption rate, geometry, turbulence…





jbaker6953 said:


> Sure it could. That could be the upper limit under conditions of near absolute stillness. Increasing circulation would only decrease the CO2 needed to saturate photosynthesis.


It sounds to me like you two are agreeing on the principle, and disagreeing on how to say it. Semantics are a frequent obstacle. Perhaps the reccuing use of the word "saturation" is the cause. After all, to saturate something is to fill it to capacity; so it's somewhat confusing to talk about saturation "levels". There is only one level of saturation - saturation .

To me it sounds like you are debating (but mostly agreeing) the minimum concentration of CO2 needed to NOT be a limiting factor during photosynthesis (with respect to light intensity, flowrate, etc).


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## windsurfer (Mar 8, 2005)

I have no problem with the concept of saturation. What I have difficulty with is the measurement technique. We’ve established that the local environment at the surface of the plant is different than that of the surrounding water because of the difficulty of transporting CO2 across the boundary layer. We also know that the amount of that difference is dependant on several variables (consumption rate, current, turbulence, bubbles, etc.). How can it be simple to define saturation of the local environment (surface of the plant) by using a measurement made on a different environment (the surrounding water) ?

I will admit this is getting boring. Do any Botonists have comments on CO2 saturation ?

-jd


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## jgc (Jul 6, 2005)

Just a currious question. We are discussion the boundry layer of the plant. Is there also a "boundry layer" surrounding the surface of a bubble? Will we also get localized co2 concentrations in that potential boundry layer?


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## unirdna (Jan 22, 2004)

jgc said:


> Is there also a "boundry layer" surrounding the surface of a bubble? Will we also get localized co2 concentrations in that potential boundry layer?


Yes, but it is not accurate to compare the boundry layer of macrophyte tissue to that created by the surface tension of water. They are not comparable, and the mechanisms creating the questions are very different.

I'm speculating why you ask, and if I'm right, I'll head off your question...

Even if a bubble of CO2 were holding completely still, with no water movement, it would still need to create a "boundary layer" of 1500ppm (saturation concentration) to stop CO2 from dissolving any further. A bubble of CO2 can not "hold" any boundary layer of concentration if it is moving, or if any current is moving past it. In fact, the law of diffusion wouldn't allow this even if the CO2 bubble was completely still (although it would take longer to dissolve).


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## Hypancistrus (Oct 28, 2004)

A couple key points I have to keep reminding myself:

O2 "saturation" in water = 12 ppm O2 (but this is actually dependant on water temperature and salinity)

CO2 "saturation" in water = 1500 ppm CO2

Photosynthesis "saturation" in plants = 30 ppm CO2

I think "maximum" would be a better word for "saturation" in that last one.


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## windsurfer (Mar 8, 2005)

Assuming I am reading things right, the references I could find in technical literature after a brief search indicate that photosynthesis saturation with CO2 is possibly much higher than 30ppm. –caveat, these papers are for saltwater plants/algae since the CO2/HCO3- relationship makes things much more complicated in our lightly buffered freshwater systems.

“High Apparent Affinity of Photosynthesis for CO2. The results presented on Figure 4, a and b show that photosynthesis of C.crispus is saturated with a little more than 330 ul/l in the gas phase, which corresponds to 150 ul/l (i.e. 5 uM) of free dissolved CO2 concentration in seawater,”


that is 150ppm 

Oxygen Uptake and Photosynthesis of the Red Macroalga, Chondrus crispus, in Seawater
EFFECTS OF LIGHT AND CO2 CONCENTRATION
Plant Physiol. (1984) 75, 919-923


Also:
“there is no apparent inhibition of photosynthesis at high CO2 concentrations”

Inorganic Carbon Source for Photosynthesis in the Seagrass Thalassia hemprichii (Ehrenb.) Aschers
Plant Physiol. (1984) 76, 776-781

That one had measurements up to 100ppm

Both these are in very high flow at saturation light levels. (there is that saturation word again).

-jd


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## jbaker6953 (Sep 18, 2005)

Saturation is not a maximum. Saturation is the point at which additions cannot be used. If a typist can type 30 wpm, and they are taking dictation, they will be saturated at 30 wpm. The speaker can talk faster, but it's not going to make them able to type faster. Same with CO2 and plants.

To say that there is no one number for saturation is to needlessly confuse the issue. You could say the same thing about my hypothetical typist. It would be like saying that there's no one number that could represent one's typing speed because it's so dependent on things like the having no broken fingers, the speaker speaking loud enough to be audible, whether the speaker is speaking the same language as the typist, whether there are any distractions in the office at the time, etc. You could say the same of anything. You could say, "how long is an inch really?" It's influenced by the temperature of the object being measured, the speed at which that object is moving (thanks Einstein), and the strength of the gravitational field in which the measurement is taken. Of course everything is influenced by variables, and those variables are the reason controlled studies are important, not a reason to discount controlled studies.

As far as photosynthesis in aquatic plants, saltwater is a very different beast. I don't know of any submerged saltwater plant. I believe there are only algae that live permanently submerged in saltwater.

I agree that the article at aquabotanic is a tenuous one as far as scientific credibility goes, but that's all there is about submerged plants as far as I can find (except for some pay journal articles).


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## unirdna (Jan 22, 2004)

jbaker6953 said:


> As far as photosynthesis in aquatic plants, saltwater is a very different beast. I don't know of any submerged saltwater plant. I believe there are only algae that live permanently submerged in saltwater.


You've been on the mark re: many aspects of CO2, jbaker. Be careful not to start discreditting yourself.

http://www.seagrasswatch.org.au/seagrass.html


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## jbaker6953 (Sep 18, 2005)

unirdna said:


> You've been on the mark re: many aspects of CO2, jbaker. Be careful not to start discreditting yourself.
> 
> http://www.seagrasswatch.org.au/seagrass.html


That's why I said, "I believe" and not "There are not." I was under the impression that sea grasses could only be submerged for short periods.


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## SCMurphy (Oct 21, 2003)

I think Ted was just teasing you jb. You guys need to use smilie's every now and again. roud:


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## windsurfer (Mar 8, 2005)

My take-away from this thread is that just getting the CO2 dissolved into the water may not be enough; you need to help get the CO2 from the water to the plant. 

To test this, I added a powerhead next to my internal CO2 reactor with it’s flow directed at a clump of pigmy chain swords that had not been growing well. I was amazed to see that not only did the chain swords quickly turn bright green and start sending out runners, but stands of Ludwigia, Rotala, and Java Fern on the opposite end of the tank (where the current went after deflecting off the front glass) also had a dramatic increase in growth rate. Pearling thru out the tank is increased. This increased growth is so dramatic that I am now having to start increasing NO2 and PO4 dosing to keep up ! After seeing this, I am now working on adding an XP3 with an external reactor to get some stuff out of the tank and provide a large increase in flow.

-jd


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## unirdna (Jan 22, 2004)

jd,

So, to clarify, you did not use the "microbubble" diffuser method, but rather, simply increased circulation (of CO2 enriched water) in your tank?


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## SCMurphy (Oct 21, 2003)

SCMurphy said:


> I'm really enjoying this debate. I wouldn't be surprised if it is just that the dispersion of dissolved CO2 is better and the across tank gradient of dissolved CO2 in ppm becomes more uniform when the micro bubbles are put into a current.


Just a little something I posted a while back in this thread.


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## windsurfer (Mar 8, 2005)

No CO2 microbubbles were introduced to the tank. just a powerhead located next to the output of my internal reactor blasting at the pigmy chain swords. 

However, when the swords pearl the bubbles get blown off before they can inflate to the normal size, so there is quite a few micro bubbles flying around the tank in the afternoon.

but again, my intention was to see the effect of increased flow -and in my case it had a very profound impact on growth.

-jd


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## Rex Grigg (Dec 10, 2002)

I have been following this thread with interest. 

Here are my thoughts.

Little bitty CO2 bubbles can't/won't last long in the water column. The bubbles we are seeing therefor are probably not CO2.

The bubbles, whatever they are, are a great indicator of water flow. We see bubbles we think are CO2 being blown all around the tank and think it's the CO2. But I feel it's more a function of the increased water movement.


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## stcyrwm (Sep 1, 2005)

Rex Grigg said:


> I have been following this thread with interest.
> 
> Here are my thoughts.
> 
> ...


A lot of this discussion is out of my league but I can say for sure that CO2 bubbles can last in the water column at least long enough to get blown around the tank. I just set up CO2 and I'm using a diffuser disc so I know my bubbles aren't anything else. I think Tom said he had already done this also to rule out other gases.


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## dennis (Feb 9, 2004)

Since laws dictate that the micro bubbles are not CO2 after ~3 seconds, logically they are N2 and O2. 

SCMurphy's comment about increased flow improving growth, along with the saturated O2 levels and micro bubbles of N2/O2 led me to wonder something.....

Either the improvment in growth is due to increased CO2 levels (assuming that freshwater macrophytes are not photosynthetically saturated at 30mg/l CO2) or it is due to presence of elevated O2/N2 levels near the leaf's surface (Pradtl boundry) 

Let's remember this, Tom reported improved growth simple by placing a diffuser in the stream from his filter. He had not increased flow so the answer here is not improved/inceased water flow. The flow remained the same in his original situation. Therefore, the improvment in growth comes from either higher CO2 levels or from something displaced/swapped by the micro bubbles.

How would micro bubbles of O2 or N2 affect the plant's grwoth?
If the growth improvment was due to an increase in dissolved CO2 (must be dissolved as the microbubbles can't be CO2, following laws of physics) wouldn't that show up as a decrease in the pH of the tank? Isn't it physically harder for a plant to optain C from CO2 gas rather than from carbonic acid?

If this is all entirely C related, would not one get the same improved growth from a higher concentration of dissolved CO2 in the water as they get from the micro bubbles? Unless, it is easier for the plant to break down CO2 gas (assuming a CO2 bubble actually gets to the plant)?


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## jgc (Jul 6, 2005)

I have heard that emergent plants do not have the co2 issue as submerged plants. Even if the micro bubbles have no more c02 concentration than the atmophere - perhaps they help submerged plants to grow more like emergent ones. Personally I would love for someone to put an airpump with a micro bubller in front of the water current and see what happens.

Personally I am using a ladder diffuser and can say with pretty much certainty that larger bubbles of co2 do not diffuse completely in 3 seconds. They continue to shrink all the way up the ladder - a path that takes the better part of a minute. The bubbles are still shrinking the last 1/3 of the ladder - where they have already been in the tank for about 30 seconds. But anyway...


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## SCMurphy (Oct 21, 2003)

dennis said:


> Since laws dictate that the micro bubbles are not CO2 after ~3 seconds, logically they are N2 and O2.
> 
> SCMurphy's comment about increased flow improving growth, along with the saturated O2 levels and micro bubbles of N2/O2 led me to wonder something.....
> 
> ...


That's not what I said. I said that:
"the dispersion of dissolved CO2 is better and the across tank gradient of dissolved CO2 in ppm becomes more uniform when the micro bubbles are put into a current." 

So what Tom did by putting his diffuser under the outflow from his filter was increase the dispersion of the dissolved CO2 throughout the tank. I didn't forget it, I picked right up on it. I did not suggest he increased flow.

I can't find where I did say that a planted tank benefits from more flow rather than less to help plants overcome the diffusion of CO2 and nutrients. I'm sure I did at some point, someplace, since that's something I agree with, but it wasn't in this thread.

It's not the micro bubbles, they are a visual indicator of the current, nothing more. The bubbles have been dismissed, completely, as having any effect on plant growth.


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## unirdna (Jan 22, 2004)

BTW, Dennis. First post! Welcome to the forum roud:


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## SCMurphy (Oct 21, 2003)

unirdna said:


> BTW, Dennis. First post! Welcome to the forum roud:


Doh! Yeah hi Dennis, welcome, btw, Willy Bemis took a job with Cornell, not Yale. He's running the Shoals Marine Lab in the summers. I'm going to go visit him next summer so I can rediscover field work. roud:


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## jgc (Jul 6, 2005)

I just can not resist beating a dead horse.

Am I incorrect in thinking that 1) the concentration of c02 in the water exceeds the atmospheric concentration. 2) the concentration of c02 in the micro bubbles can not be less than the concentration of co2 in the water 3) hydroponics growers use enriched atmospheric co2 concentrations increase growth in terrestrial plants (or at least one recreational terrestrial plant), and 4) some aquatic plants find it easier to adsorb atmospheric co2 rather than dissolved co2) 

Anyway, please correct me if any of those assumptions are incorrect. 

It just seems to me that there has been way too little testing done to totally dismiss any possibility that Tom’s (sorry, I initially named the author incorrectly) initially observations of increased plant growth with a micro bubble diffuser placed in the current as complete hogwash.

--- 
Here are my bets given my previous assumptions. 1) In a non-enriched tank, micro-bubbles of compressed air will increase growth in some plants (those that normally will grow immersed) I am curious to what extent, if any, it will help normally submerged plants. 2) Plants that benefited in #1 will also benefit when co2 is introduced via micro-bubbles in an otherwise co2 enriched tank.


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## unirdna (Jan 22, 2004)

1) False, atmosphere contains 300ppm CO2

2) False, concentration of microbubbles can be several thousand ppm CO2 (and still resist dissolving). If equilibrium of atmospheric CO2 (300ppm) is at .5ppm with water, then for a tank containing 30ppm CO2, that same gas equilibrium would be 18000 ppm. However, if the bubble is all CO2, it will dissolve completely, unless other gasses diffuse into the bubble. In order to avoid confusion, you need to fully understand what PPM means. PPM is a concentration level with respect to the whole, not a flat number. According to Henry's law, once the CO2 concentration is lowered to 18,000 ppm, it will no longer readily dissolve into water (that contains 30ppm CO2). If you have trouble wrapping your mind around this concept, consider the following. The air has 300ppm CO2. But can you increase CO2 to 300ppm in water by bubbling air into it? Certainly not. Gas laws are esoteric, but they are quite real.

3) True. But, consider the above post. The more CO2 you have in the air, the higher the equilibrium (ppm) that enriched air has with water. So, the water within the plant tissues will more readily "soak" up gasseous CO2 if the concentration in the air is higher.

4) Many aquatic plants attempt to interface with the atmosphere to gain access to more readily available CO2. Emergent plants have a very real advantage.


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## SCMurphy (Oct 21, 2003)

jgc said:


> It just seems to me that there has been way too little testing done to totally dismiss any possibility that Rex’s initially observations of increased plant growth with a micro bubble diffuser placed in the current as complete hogwash.


It wasn't Rex it was Tom. We didn't dismiss the increased plant growth, we did a better job of explaining it.


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## jgc (Jul 6, 2005)

Thank you for the corrections. I will edit my original post to protect the names of Tom & Rex

My points were basically. 1) If emergent plants have an advantage – in a non-co2 enriched tank micro-bubble of air might simulate emergent growth. 2) Emergent growth in co2 enriched air might be greater than in non-enriched air. 3) Persistent micro-bubbles in an enriched tank (even though they are primarily other gasses) should still have a greater than atmospheric concentration of co2.

Will add that even if we inject micro bubbles of air into an enriched tank, co2 dissolved in the water would try to achieve equilibrium with the air in the bubble and the bubble would end up having a greater than atmospheric co2 concentration.

Oh well, will try to step away from the horse again.


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## defdac (Dec 28, 2003)

jgc said:


> Will add that even if we inject micro bubbles of air into an enriched tank, co2 dissolved in the water would try to achieve equilibrium with the air in the bubble and the bubble would end up having a greater than atmospheric co2 concentration.


Exactly my thought also.

So even if the micro bubbles are other gases and they land under leaves, they will "soak up" CO2 from water and remove the prandtl-layer and you have in fact a high CO2-atmosphere without a layer near the stomatas maknig the plants grow faster?


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## Opiesilver (Nov 3, 2003)

defdac said:


> Exactly my thought also.
> 
> So even if the micro bubbles are other gases and they land under leaves, they will "soak up" CO2 from water and remove the prandtl-layer and you have in fact a high CO2-atmosphere without a layer near the stomatas making the plants grow faster?


Now that I agree with. By putting the micro-bubbler in the water current path you also increase the water contact time with the bubbles which helps increase the CO2 absorption rate. That will help with stabilizing and maintaining higher CO2 levels in the water column.

Yes Dennis, it is easier for plants to absorb carbon from carbonic acid (H2CO3) rather than strait CO2. However in the presence of water, H2O, carbonic acid very quickly breaks down into H2O and CO2 while in a non-equalized state. I read a paper a few years ago, which I think came out of Europe somewhere, that calculated that just two water molecules together can increase the rate of decomposition of carbonic acid by a factor of 50 billion. Without the presence of a catalyst, like H2O, carbonic acid is a pretty stable compound. Now this may be a far stretch but this leads me to believe that true aquatic plants have evolved a way to utilize CO2 gas more efficiently than their emergent cousins that rely on a strategy of breaking the water surface for faster growth. We should be able to see very different underwater growth results between the two classes of plants in this kind of experiment.


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## unirdna (Jan 22, 2004)

jgc said:


> Will add that even if we inject micro bubbles of air into an enriched tank, co2 dissolved in the water would try to achieve equilibrium with the air in the bubble and the bubble would end up having a greater than atmospheric co2 concentration.


Agreed. Although I don't know that this would result in increased growth. And when I say "I don't know", I do not mean "I belive it would not" , I mean "I don't know". We need to better understand plant physiology before constructing hypotheses. And remember to study up hard, because as we've seen on this thread already, a little bit of knowledge can be dangerous.

I think we've turned the corner on this discussion. 

Next step: 

1) Do CO2 "enriched" (1.8% for a tank containing 30ppm CO2 in aqueous solution) microbubbles - resting on the underside of plant leaves - improve growth? How? Why? How much? And I say "resting on plant leaves" because those bubbles of gas containing 18000 ppm CO2 are still at equilibrium with the solution. They will not "carry" that CO2 around the tank, and disperse it slowly. They are "keeping" their CO2 gas. Furthermore, as more 02 diffuses into the bubble the PPM of CO2 will be lowered further, creating a bubble that is "hungry" for CO2. This "enriched" bubble discussion is a moot point unless the bubbles come in direct contact with plant tissue.

2) Does increased circulation improve growth? How? Why? How much circulation? How much plant growth? This one, we've suspected all along to be a major contributer, since diffusion alone can be a bit sluggish. However, we should approach the question with the same scientific vigor as more esoteric questions.


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## jgc (Jul 6, 2005)

I have one last thought, till I leave this to the experts for a while. How long does it take a c02 bubble or an air bubble to achieve equilbrium given the aggitation a suspended (or captured) bubble recieves. Depending on the time, the captured bublles will probably not be at equalibrium, but perhaps several % away from it. Course depending on how much away, it may have no net effect.

The first big if is do enriched bubbles even help, the second question then comes into being - how enriched are the actual bubbles.


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## IUnknown (Feb 5, 2003)

Tom wrote:
"The only way to add more than 100% ambient levels is through plant production."

What about injecting O2? I still have to read most of the other threads on this subject but was curious as to the conclusion of the "Co2 actaully being O2 bubbles" issue. It seems like the best way to disprove that would be to run the diffusser in a tank without plants (maybe this was done?). If the DO meter measures an increase in Oxygen levels then this would show that the Co2 bubbles are actually being filled up by O2 as the Co2 diffusses out. The idea is that the Co2 bubbles would be sucking Oxygen from the surface of the tank to over saturate the tank(were else would the O2 come from?). This would explain why the bubbles persist more later in the day as the tank is saturated with O2.

The other issue that I'm not convinced about is 30ppm being saturated enough to slow down the rate of diffussion. This thread did a pretty good job of disproving that idea,"CO2 Solubility Experiment - Photos, Video.....Evidence! " . I guess you could connect a ph meter to a computer to see if the absorption rate changes at all. If it doesn't the Co2 would be a line in a ph vs time chart. It would be a bell curve if 30 ppm slowed down the saturation rate.

I've got a difusser in the mail to see how things improve. Regardless of whats actually happening the extra O2 is good for feeding bacteria, etc. Interesting stuff, I'm glad you have a thick enough skin to deal with all the attacks Tom, the hobby would not be going anywhere otherwise.


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## plantbrain (Dec 15, 2003)

Well, besides adding pure O2, you cannot get above 100% with aeration , filtration, current etc.

Taken out of context in the quote is a bit misleading.........

Adding pure O2 btw will not make you plant pearl more, it's much more localized issue and the production from the plants themselves on the surfaces that drives the gas out. Not saturation levels.

I've used pure O2 a fair amount in plant tanks and with algae experiments.

The CO2 issue is really something you need to try out.
I'll conceed some solubility but the time rate I measured was lower at 30ppm than at 1.5 ppm at the KH of 2.

KH influences the solubility of CO2 FYI.

The method is relatively easy to test:

Use a Dissolved O2 meter and measure the CO2 for each treatment.

1. Tank CO2: 30ppm Add mist hitting plants
2. Tank CO2: 30ppm No mist hitting plants 

Next, switch the mist on/off in tank one.
If the DO level is higher in #1 with the mist, then it's safe to assume that the mist effect is significant.

To date, as I much expected, not one person(other than myself) has done this experiment:icon_roll 

So.........

I'l redo the experiment and get a very good record of the data for each parameter and put it out there for folks to consider.

I got 30-40% more O2 the first time.

Gas does not dissolved into solution insteanously either.
Some want to believe so.
Takes a few seconds and by then the bubble has hit the plant and broken into the boundary layer.

Regards, 
Tom Barr


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## fresh_lynny (Mar 9, 2006)

Rex Grigg said:


> I personally am getting a huge kick out of this thread. I don't see it as attacks.
> 
> If someone, anyone, wants to come in and make statements or claims then they should be prepared to back them up. All to often people come to this forum and make claims about things. When questioned they either leave, clam up, or lie.
> 
> This is nothing but a very civil scientific debate.


Strongly agreed!

Scientific debate is how we learn. No one involved should have a thin skin here. No one is "attacking" credibility. I, for one, appreciate the many contributions made by Tom, but scientifically, I agree with Ted on this point. This in no way discredits anyone, it merely helps us all reach an understanding as to why something is the way it is. Hypothesis are one thing, but scientific fact is another, and healthy debate on that front is something even Tom Barr can appreciate, despite which side it is on.


ok well I am late with this....but I love this thread!!! many good points. Keep up the brainstorming!


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## banderbe (Oct 10, 2005)

plantbrain where can I get good venturi reactor design?

your website just has pictures and diagrams.. would be nice to see step by step.. I am not very happy with limewood airstones... they are okay but it is hard to circulate the bubbles.. I could use a powerhead.. but your venturi is more than just that right?


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## Hoppy (Dec 24, 2005)

I have a viewtainer on order, and a new powerhead ordered from ebay, which I will use to build Tom's venturi reactor, as I understand it. I don't think I am getting enough CO2 dissolved into the water with my mist system, so I plan to use the venturi device in my soon to be set up 45 gallon tank. I agree with Barry that a more detailed sketch or photos would be very helpful.


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## plantbrain (Dec 15, 2003)

It recirculates the caught bubble and atomizes it as it builds up.
Any loop can do this that has a reaction chamber.

An issue with Ted's experiment:
The micro bubble and a reactor filled with CO2 are two different situations, I'm not saying CO2 does not disolve rapidly, never did state that.

I'm saying it has enough time to hit the plant and be absorbed or dissolve at very high levels in the plant's boundary layer.

Another issue:KH.

CO2 is far more souble at higher KH's, 15 is a long way from 1 KH.
The solubility of CO2 increases with increasing pH(due to alkalinity).

So repeat the experiment with some RO or DI water.
You should get a different time to dissolve the same CO2 volume.

We are not talking about several minutes, rather, seconds.
The small microbubble mist has different properties than a large bottle shaken for a few seconds.

All CO2 goes into aqueous phase prior to assimilation, that is true for us as well, we release CO2 from the liquid phase tro the gas phase when we breath.

The presence of other substances alos influences things. The solubility tends to decrease with concentration of "inert" ionic solutes like sodium chloride, but may increase or decrease with increasing concentration of organic compounds.

Why does CO2 not "instantly" dissolve?

While some evidence does suggest that the CO2 does in fact dissolve rapidly, no one is arguing that it does not here, what is in that same CO2 bubble that does persist for 30 seconds?

I'm not talking about large jar test, that does not answer the question.
I cannot really chase these micro bubbles around and analyze them over short time frames easily.

CO2 will diffuse out of the bubble, we can watch the CO2 mist rise and dissappear. Now why do these same bubbles persist late in the day?

I added pure O2 above ambient air saturation(15ppm @ 28C, roughly 200%) and the CO2 mist bubbles still dissolved rapidly, so it's not O2 going into there.

What gas is maintaining the micro bubble that are left?
The water is not saturated with any gas in particular.

If N2 or O2 can diffuse into the bubble at a given rate, so can CO2, which is still at 30ppm etc.

Then it's an issue of phase, gas vs aqueous.

And when it comes top phases, we know which is much faster at uptake: the gas phase is 10,000times faster.

So even if the gas in those micro bubbles is not pure CO2, it's still going to have similar CO2 ppm as the water around it.

So the flux into the plant is mediated by gas rather than liquid exchange, try and breath water sometime and see how much harder it is to exchange the O2/CO2.

Still, rather than chasing micro bubbles, simply maintaining good CO2 ppm for 2 treatments at stable levels and then add/delete the CO2 mist and measure the O2 response, since plant growth is really the end result we are most interested in, will tell you if the method works and that the gas phase is likely a responsibile agent.

Regards, 
Tom Barr











depending upon the compound.


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## IUnknown (Feb 5, 2003)

Hoppy,
I'm going to try the Mazzi injectors eventually on Tom's recommendation. I'm using a glass Lillie so it would sit inline right before the glass outlet. Have to play around to get it to look nice with a ball valve and tee's, etc. Picture this verticle before the outlet,


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## Betowess (Dec 9, 2004)

Iunknown, Could you explain what is the "Mazzi injector"? It kind of looks like a type of CO2 manifold, with a ball valve to control flow. I take it the blue line is a CO2 gas line running into this device. And the outflow is obviously on the right as you said it's oriented vertically... Is this some kind of alternative reactor deal? And you run this into your lily output (or a spraybar etc?) Thanks.


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## IUnknown (Feb 5, 2003)

Check out there website, shows some pictures of the venturi. It is used to mist the Co2 into the tank, replacing a reactor that would be dissolving the Co2 into the tank. You would run this right before your output or spray bar, closer the better to keep the Co2 in bubble form. Haven't tried it yet, so don't know if it would be any better than a diffusser.

Mazzei Injector Corp. - How a Mazzei Injector Works


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## Hoppy (Dec 24, 2005)

I can't see the theory behind this being a better method of injecting CO2 into a water flow than just sticking a CO2 tube into the side of the water line. Very few of us would use a water pump that would build up much pressure in the water line - a maximum of maybe 1/10th of an atmosphere (3+ feet of head). Pressurized CO2 would easily overcome that. The only thing I see as a possible advantage is that the CO2 bubble would enter at a "low" pressure, then flow into a higher pressure region, which would shrink the bubble to make it more of a microbubble. The system Tom is using on his 1600 gallon tank uses much more advanced water pumps, which probably do generate a higher pressure where the venturi is mounted. Am I missing something?


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## rey (May 17, 2005)

Now, this looks like a topic for a new thread...
I'd love to know how one of these "venturi valves" 
as they used to be called by reefers would work for CO2.
In addition to Mazzei, Kent also makes one...also
those waterbed fill kits have a similar device.
Anybody know how much these things would slow down
an Eheim?


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## Hoppy (Dec 24, 2005)

The waterbed pump is a jet pump, slightly different from a venturi. I use one for my water changes, and I doubt it having a measurable effect on filter output flow. Yes, a new thread would be nice.


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## IUnknown (Feb 5, 2003)

OK moved it to scolley's old thread,

http://www.plantedtank.net/forums/diy/21735-diy-line-micro-bubbler-5.html


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## unirdna (Jan 22, 2004)

*Resurrection - Finally giving it a try.*

Well, I finally got around to doing my own experiment. There was more delay than I wanted, but that's life.

Tank Specs:
10g, 50w PC lighting, CO2 60 bpm injected into a duetto filter (20-30ppm according the pH/KH calculations).

There is mist flying all over the tank, and much of it is collecting on the undersides of leaves. I have "stocked: the tank with a hand full of hygro, a small lotus, and a few sprigs of HC. Substrate is a 1.5 bags of EcoComplete. 

As of day 3, there is no algae and plant vitality/growth is very good.

While we may continue to debate the dissolution properties of CO2, I am more than hopeful that this misting effect offers an improvement over reactors - whatever the cause.

Trying to do my part to move the hobby forward. So far, so good.

Ted


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