# CO2 and surface agitation?



## zergling

Surface agitation is always good, as long as it's not stupid crazy amounts in a high light tank where you're degassing CO2 in the same rate as you're injecting it. 

In low-light tanks, you want good surface movement to prevent/minimize surface film and have good air exchange at the surface (especially important at lights off where the plants are not producing O2).

I don't know if anyone has done a nutrient breakdown analysis of aqua soil and potting soil. Hopefully someone chimes in here if that kind of research already exists. 
I think folks here in TPT have done well with all sorts of substrates. I personally now use aqua soil in all of my tanks due to ease of use and not having to deal with layers of different stuff getting all mixed and messed up.


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## fish h20

My plants grow better with no surface agitation. When I ripple the surface my submerged plants almost stop growing. I think snails eat surface film. Mine are always cruzing the surface.


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## Harry Muscle

For non CO2 injected tanks surface agitation actually increases the amount of CO2 in the water. For CO2 injected tanks surface agitation decreases the amount of CO2 in the water.

Thanks,
Harry


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## lauraleellbp

I think it's unlikely that CO2 produced by soil decomp would increase CO2 levels higher than good circulation would? Though IDK that for sure...

The thing about poor circulation is it leaves more work for you keeping a tank clean of debris buildup, and decomposing debris typically encourages algae.

I maintain pretty high circulation and/or surface agitation on all of my (non CO2) tanks.


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## FriendsNotFood

Harry Muscle said:


> For non CO2 injected tanks surface agitation actually increases the amount of CO2 in the water. For CO2 injected tanks surface agitation decreases the amount of CO2 in the water.
> 
> Thanks,
> Harry


By this logic, would adding an airstone increase CO2 concentration in a non-CO2 tank?


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## VeeSe

FriendsNotFood said:


> By this logic, would adding an airstone increase CO2 concentration in a non-CO2 tank?


Yeah, it's possible if the plants are taking up a decent amount. If it's just lightly planted then there's probably very little difference.


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## fish h20

I am no planted tank expert but the way I understand it organic decomp can produce a good bit of CO2. The CO2 in the water could be at around 10 PPM or so in the morning. The highest I understand you will see with say a airstone in the tank is .5 PPM (atmospheric equilibration). If you are curious it is page 100 in "Ecology of the Planted Aquarium". Remember you are in a forum where everyone acts like they know everything but very few of them know anything. At least I start by telling you I don't know it all. I know you can't believe everything you read either so, as I stated earlier, I have proven this to myself. I had an airstone and my plants did not do well at all. I removed it and my hang on back filter and replaced them with a canister filter and very little surface agitation and my plants took off in a matter of a few days. There are a lot of variables in this stuff and I am not saying it will work for you but I encourge you to try it both ways for yourself and see what you find is better for you. 
You could also try PM'ing Tom Barr on this subject. He is a pretty trusted source by most.
One bad thing about no or very little agitation is the CO2 will rise and fall (fluctuate). It will be steady with heavy surface agitation.
Good luck, I wish you the best. I hope this helps you in some way.


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## FriendsNotFood

That is indeed helpful, thanks fish. I know Tom does very little water changes on his non-CO2 tanks to keep the CO2 levels constant, but I don't know what he uses for surface agitation, if any. Guess I'll wait for him to chime in (;

I was hoping someone would answer my related question about Aquasoil vs. dirt... does dirt produce much more CO2 than Aquasoil since Aquasoil is intended for tanks with added CO2?

I'm not stripping down my tank or anything, was just wondering this stuff for improving my general understanding of low-tech tanks and hopefully growing happier plants


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## Byron

> For non CO2 injected tanks surface agitation actually increases the amount of CO2 in the water.


I do not understand how this can be. Surface disturbance at any level will drive CO2 out of the water and draw in oxygen. Air bubbling devices, airstone, etc. in the tank do the same. I have never read anywhere that CO2 enters the water via the surface movement.

And as the aim in a non-CO2 system is to create and preserve as much CO2 as possible, this would seem to require less water movement especially at the surface.

Byron.


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## meowfish

Harry Muscle said:


> For non CO2 injected tanks surface agitation actually increases the amount of CO2 in the water.


Your theory is sound, but this isn't true in practice because air is 21% oxygen, 78% nitrogen, and 1% trace gases. There's virtually no CO2 (like 0.03%) to dissolve into the water no matter how much surface agitation there you have.


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## lauraleellbp

meowfish said:


> Your theory is sound, but this isn't true in practice because air is 21% oxygen, 78% nitrogen, and 1% trace gases. There's virtually no CO2 (like 0.03%) to dissolve into the water no matter how much surface agitation there you have.


There are some older threads on here that go into detail with the mathematics of why you are incorrect, I don't recall the numbers offhand, but I'm sure a little searching and you'll pull them up.

However, the relative concentration of CO2 in the atmosphere in most cases is going to be higher than the concentration of CO2 in a non-CO2-injected aquarium, so increasing the exposure of the water to air will in fact bring a tank more into equilibrium with the concentration in the atmosphere and will raise the CO2 concentration. A tank with good circulation will therefore usually have more CO2 in the water than a stagnant one. 

There are other benefits of good circulation in tanks beyond just CO2 levels that to me are more significant (better filtration, better oxygen content, less risk of anaerobic spots/hydrogen sulfide development, etc), so IMO there's just no downside to having good circulation going in a planted tank.


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## meowfish

lauraleellbp said:


> the relative concentration of CO2 in the atmosphere in most cases is going to be higher than the concentration of CO2 in a non-CO2-injected aquarium, so increasing the exposure of the water to air will in fact bring a tank more into equilibrium with the concentration in the atmosphere and will raise the CO2 concentration.


Potentially, though this is more of a linguistic technicality. I should have been more concise - what I intended to convey was that more surface agitation doesn't raise the CO2 concentration proportionally, and in fact can never raise it any higher than the ambient concentration (meaning the same as "equilibrium" in context of your response).



lauraleellbp said:


> A tank with good circulation will therefore usually have more CO2 in the water than a stagnant one.


Not necessarily. If CO2 is any higher than the ambient concentration to begin with (regardless of source), surface agitation will lower the CO2 concentration. If we're talking water and gravel in a still aquarium with no critters (microscopic or otherwise) I'd agree completely. Again, the theory is sound, but there's a lot of consumption/production variables in the mix. I'll do some searching for the posts you mentioned and see if they take all of them into account - if so I may have to recant. 



lauraleellbp said:


> There are other benefits of good circulation in tanks beyond just CO2 levels that to me are more significant (better filtration, better oxygen content, less risk of anaerobic spots/hydrogen sulfide development, etc), so IMO there's just no downside to having good circulation going in a planted tank.


Seconded - my comment was regarding surface agitation, but I think you make a very important point. I know this forum has seen numerous enjoyable debates on that topic as well!


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## Meme2012

*Fluval Roma 90L - contraditions to what is required*

Hi - I have just bought a 90L tank for Tropical fish, i have an E Series 100 heater, U3 Underwater Filter (change from a U2 Filter as advised by the store - so i have two now, one is going to be for emergencies) but do i also need an airpump?

I was not told this in the shop and 4 of my fish have died. I have rehomed them in my old smaller tank which i kept going. 

I am not techi at all but having read through loads of posts this is the nearest to my query, please can someone help as if i go in store they will just sell me stuff i either don't need again.

Please help!:icon_frow


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## fish h20

I googled CO2 in the atmosphere and it is 390 PPM. We should all get airstones for our aquariums! Someone with not enough information is just as dangerous as someone with none.:icon_wink


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## fish h20

lauraleellbp said:


> There are other benefits of good circulation in tanks beyond just CO2 levels that to me are more significant (better filtration, better oxygen content, less risk of anaerobic spots/hydrogen sulfide development, etc), so IMO there's just no downside to having good circulation going in a planted tank.


Circulation and surface agitation are two different things. No one is saying circulation isn't good.


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## FriendsNotFood

I went ahead and PMed Tom Barr. He says that both surface agitation and water circulation are beneficial in a non-CO2 tank, perhaps even more so than in other setups. Guess I'll move my spraybar back to the surface then.


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## galabar

fish h20 said:


> I am no planted tank expert but the way I understand it organic decomp can produce a good bit of CO2. The CO2 in the water could be at around 10 PPM or so in the morning. The highest I understand you will see with say a airstone in the tank is .5 PPM (atmospheric equilibration). If you are curious it is page 100 in "Ecology of the Planted Aquarium". Remember you are in a forum where everyone acts like they know everything but very few of them know anything. At least I start by telling you I don't know it all. I know you can't believe everything you read either so, as I stated earlier, I have proven this to myself. I had an airstone and my plants did not do well at all. I removed it and my hang on back filter and replaced them with a canister filter and very little surface agitation and my plants took off in a matter of a few days. There are a lot of variables in this stuff and I am not saying it will work for you but I encourge you to try it both ways for yourself and see what you find is better for you.
> You could also try PM'ing Tom Barr on this subject. He is a pretty trusted source by most.
> One bad thing about no or very little agitation is the CO2 will rise and fall (fluctuate). It will be steady with heavy surface agitation.
> Good luck, I wish you the best. I hope this helps you in some way.


I like your post. 

This should be fairly easily testable. There are various kits out there that will give you CO2 ppm. Also, you can fiddle with your drop checker reference solution to determine CO2 concentrations.

I believe it is correct that a non-CO2 injected, well aerated tank (through surface agitation or airstone) will be at around 0.7 ppm. It may be difficult to test values that low. However, if a "stagnant" (no surface agitation) tank increases to 10 ppm, we can test for that.

Now, if that is the case, it doesn't mater what Tom Barr or anyone says. 10 ppm is going to grow your plants much faster than 0.7 ppm, even in a low light, low tech tank.  We know what your CO2 concentration will be with surface agitation or an airstone. We don't know what it will be without surface agitation -- we need to check that value before we make definitive statements (and no one has checked so no one should be making definitive statements).

p.s. In a CO2 injected tank, there is no question. I went from two Emperor 280 HOB filters to a canister filter (pointing the spray bar 45 degrees down, rather than at the surface). My in-tank reactor went from needing 2 bps to only needing 0.1 bps, a 20X reduction!


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## Byron

This is still very unclear. For years it has been maintained that surface disturbance drives out CO2 and brings in oxygen, the gaseous exchange. Increasing surface movement would therefore seem to be contrary to the goal in a natural (non-CO2) system of retaining CO2 in the water for the plants. Is there evidence this is not correct?


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## FriendsNotFood

Someone here want to measure this? I don't have any CO2-measuring equipment. BTW I assume we're not talking about *stagnant* tanks, just ones where there is little surface disturbance but plenty of circulation.


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## Daximus

I think we can all accept that a given body of water and the atmosphere will reach an equilibrium of some sort in regards to whatever gasses we are considering. If you all tell me that magic number is .5 or .7 ppm with regards to Co2 then I'll take your word for it. I'm not that smart. 

I think we can also all accept that the act of breaking the tension (the skin, if you will) of the water or greatly increasing it's surface area (though agitation) will speed up this equilibrium process. 

But that's just it, an equilibrium process. It's not like Co2 is allergic to water and all of it is dying to escape, no, it's just reaching whatever that natural equilibrium is. So, my contention and theory on the different results is all the minute differences that perhaps we are passing over. 

Is it a dirt tank naturally creating some unknown amount of Co2 through decomposition?

Is it heavily planted enough with enough light to drive the plants to need more Co2 than provided at atmospheric/water equilibrium?

And last, but certainly not least...does it gots any fishys, lol? Last I checked those little suckers breath in o2 and out Co2. 

If something inside your tank is creating, breathing out, or injecting more Co2 than naturally found at equilibrium then overly agitating/breaking the water will result in faster gas off. 

If something inside you tank is depleting Co2 faster than might be achieved by natural equilibrium then, said agitation and breaking water will probably result in faster "gas in." 


Fully knowing I could be totally wrong, I shall return the discussion back to y'all, lol. :hihi:

I suspect the first "if" is more common than the second.


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## Byron

Thank you Daximus, this goes a long way to explain things.:thumbsup:


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## Daximus

Byron said:


> Thank you Daximus, this goes a long way to explain things.:thumbsup:


Easy now, that's my theory. I'm not saying any of that is factual, lol. :hihi:


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## ItsDubC

To add to this discussion, aren't CO2 levels in a tank much higher in the morning after a night of no photosynthesis occurring (or whatever your photoperiod schedule is)? I would think that constant surface agitation throughout the night would prevent this plant-beneficial CO2 build-up from happening.


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## lauraleellbp

ItsDubC said:


> To add to this discussion, aren't CO2 levels in a tank much higher in the morning after a night of no photosynthesis occurring (or whatever your photoperiod schedule is)? I would think that constant surface agitation throughout the night would prevent this plant-beneficial CO2 build-up from happening.


It's not that simple, since in the absence of light plants ABSORB O2 and RELEASE CO2.

Daximus explained pretty well that there are quite a few factors that will influence actual CO2 levels from setup to setup.

It should also be noted that most hobbyist-grade CO2-measuring equipment is fairly inaccurate. Tom Barr has access to lab-grade CO2 measuring equipment and has tested CO2 levels across different setups pretty extensively, and personally I am satisfied with his conclusion that for *most* heavily planted non-injected setups, the more circulation/surface agitation, the better for the CO2 levels.


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## ItsDubC

lauraleellbp said:


> ...since in the absence of light plants ABSORB O2 and RELEASE CO2.


I'm confused. Aren't we agreeing? lol

Maybe my Benedryl from last night hasn't worn off yet...


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## galabar

lauraleellbp said:


> It's not that simple, since in the absence of light plants ABSORB O2 and RELEASE CO2.
> 
> Daximus explained pretty well that there are quite a few factors that will influence actual CO2 levels from setup to setup.
> 
> It should also be noted that most hobbyist-grade CO2-measuring equipment is fairly inaccurate. Tom Barr has access to lab-grade CO2 measuring equipment and has tested CO2 levels across different setups pretty extensively, and personally I am satisfied with his conclusion that for *most* heavily planted non-injected setups, the more circulation/surface agitation, the better for the CO2 levels.


First, aren't plants always resperating (turning O2 into CO2)? It is only during photosynthesis that the CO2->O2 production outweighs the O2->CO2 production.

Now, you are giving us new information. You claim that Tom Barr provided you with information about tests and measurements he's done with various tank setups. Can you share this information? Can Tom?


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## Byron

ItsDubC said:


> To add to this discussion, aren't CO2 levels in a tank much higher in the morning after a night of no photosynthesis occurring (or whatever your photoperiod schedule is)? I would think that constant surface agitation throughout the night would prevent this plant-beneficial CO2 build-up from happening.


This is correct. CO2 occurs from the continual respiration of fish and plants. But the majority of CO2, far greater than from respiration, occurs from the breakdown of organics by bacteria primarily in the substrate. This is why the pH is lowest just when the tank lights come on (= at the end of the period of darkness) due to the increase of CO2 which creates carbonic acid, lowering the pH. During the day, as the CO2 is used by plants the pH rises to be at its highest at the end of the period of light. This diurnal fluctuation occurs in natural waters, and in the aquarium it is more significant due to the confined space. We have far more plants (and fish) per volume.

Some time back I had this discussion with Tom, and he pointed out the above. Hee mentioned that the available CO2 is often exhausted to a level below that required by plants to fully photosynthesize during the light period, and this will then limit their growth, and algae will take advantage to increase if light continues.

I know this occurs in my planted tanks. The pH rises roughly by 3 to 5 decimal pioints during the day (light) and then falls back during darkness. I do not have CO2 addition, and I have very minimal surface disturbance.

I am still skeptical of how surface disturbance will bring in more CO2 in this situation. Earlier posts have explained the rationale, so that is clearer; but this does not mean it occurs. Water in equalibrium with air contains 0.5 mg per litre of CO2. With the above processes continuing, I cannot see how the CO2 in the air could be greater than what is in the water. While the reduced CO2 may not be sufficient for plants to photosynthesize, it is still present. Thus, surface distrubance would tend to drive out CO2. I would welcome any evidence to the contrary.

Byron.


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## Hoppy

Does anyone have a reference to the concentration of CO2 in water in equilibrium with the air? It used to be assumed that that was about 3 ppm. I once did some testing and was able to see the concentration drop below 3 ppm. Now, I'm reading here that it is .5 or .7 ppm, but with no reference to testing that shows that.

The reason water surface rippling can increase the concentration of CO2 in the water, for a non-CO2 injected tank, is the increased surface area and reduction in surface film, which will improve the rate of absorption of CO2 from the air to replace that used by the plants. I don't know of anyone actually testing this hypothesis, so it remains just that.

Also, there aren't several methods for measuring the concentration of CO2 in water, unless the water has nothing in it to affect pH except carbonates and CO2. Then there is one easy method - measure pH and KH - which is much harder in practice than in theory. Few people can see small color differences involved in titration pH measurements which correspond to very significant differences in CO2 concentration. And, measuring KH accurately requires careful accurate calibration of the test kit, something few people ever do.


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## galabar

Byron said:


> This is correct. CO2 occurs from the continual respiration of fish and plants. But the majority of CO2, far greater than from respiration, occurs from the breakdown of organics by bacteria primarily in the substrate. This is why the pH is lowest just when the tank lights come on (= at the end of the period of darkness) due to the increase of CO2 which creates carbonic acid, lowering the pH. During the day, as the CO2 is used by plants the pH rises to be at its highest at the end of the period of light. This diurnal fluctuation occurs in natural waters, and in the aquarium it is more significant due to the confined space. We have far more plants (and fish) per volume.
> 
> Some time back I had this discussion with Tom, and he pointed out the above. Hee mentioned that the available CO2 is often exhausted to a level below that required by plants to fully photosynthesize during the light period, and this will then limit their growth, and algae will take advantage to increase if light continues.
> 
> I know this occurs in my planted tanks. The pH rises roughly by 3 to 5 decimal pioints during the day (light) and then falls back during darkness. I do not have CO2 addition, and I have very minimal surface disturbance.
> 
> I am still skeptical of how surface disturbance will bring in more CO2 in this situation. Earlier posts have explained the rationale, so that is clearer; but this does not mean it occurs. Water in equalibrium with air contains 0.5 mg per litre of CO2. With the above processes continuing, I cannot see how the CO2 in the air could be greater than what is in the water. While the reduced CO2 may not be sufficient for plants to photosynthesize, it is still present. Thus, surface distrubance would tend to drive out CO2. I would welcome any evidence to the contrary.
> 
> Byron.


First, here is some information:



> However, reguardess of the alkalinity, when CO2 equilibration occurs between water and air the partial pressure of CO2 in the water will equal the partial pressure of CO2 in the air. Assuming that air contains only about 400 ppm of CO2, the concentration of CO2 in water at equilibrium will approach 0.7 ppm ( Rainwater and Thatcher 1960).


http://www.aslo.org/lo/toc/vol_12/issue_4/0568.pdf

So, aerating your tank will tend to cause it to have CO2 at about 0.7 ppm. This means that a well aerated tank (without CO2 injection) will always present 0.7 ppm of CO2 to plants.

Now, let's imagine a tank with no surface agitation. At night fish and plant respiration will causes CO2 levels to rise. Bacterial respiration will causes this to rise even further (probably significantly more than the fish and plants, put reference needed  ). If this gets really "high," say 10 ppm (as was claimed by someone in a previous post), this may aid significantly in plant growth. Even if the plants use up most of this CO2 during the day, and eventually lower the CO2 concentration to less than 0.7 ppm, you might expect to see a significant boost in plant growth.

Let's now change our assumptions. Let's assume that the nightly respiration only increases CO2 concentration to, say, 1 ppm. This will slightly increase plant growth initially, but the plants in this scenario may deplete the CO2 concentration to below 0.7 ppm much more quickly, showing slower overall growth.

So, I think there needs to be more testing in this area. We need to know the concentration of CO2 when the lights come on, when that concentration hits 0.7 ppm, and how low it goes before the lights go off.


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## AirstoND

Just thought I'd say if you have a gas stove (relatively high CO2 source even if turned off) and aquarium is nearby, 

Can you dissolve more CO2 into water with surface agitation?

Is there a CO2 solubility equation somewhere for water as a function of temperature and CO2 in room with gas stove?


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## Chlorophile

I disagree with anyone who says surface agitation increases co2 in tanks without co2 injection.

The co2 in the atmopshere is 390 and it will reach equilibrium with water pretty quickly - the equilibrium is around 4ppm in water at 390ppm in air. 
Agitation will only force the water to reach this equilibrium faster. 

Minimal agitation a long with biological processes from bacteria and fish will raise the co2 in a low-tech tank to levels greater than the equilibrium point - stagnant surface water will keep them that way. 

You still need flow in the tank to move the gasses around, but you don't want much surface agitation at all.


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## Chlorophile

Daximus said:


> I think we can all accept that a given body of water and the atmosphere will reach an equilibrium of some sort in regards to whatever gasses we are considering. If you all tell me that magic number is .5 or .7 ppm with regards to Co2 then I'll take your word for it. I'm not that smart.
> 
> I think we can also all accept that the act of breaking the tension (the skin, if you will) of the water or greatly increasing it's surface area (though agitation) will speed up this equilibrium process.
> 
> But that's just it, an equilibrium process. It's not like Co2 is allergic to water and all of it is dying to escape, no, it's just reaching whatever that natural equilibrium is. So, my contention and theory on the different results is all the minute differences that perhaps we are passing over.
> 
> Is it a dirt tank naturally creating some unknown amount of Co2 through decomposition?
> 
> Is it heavily planted enough with enough light to drive the plants to need more Co2 than provided at atmospheric/water equilibrium?
> 
> And last, but certainly not least...does it gots any fishys, lol? Last I checked those little suckers breath in o2 and out Co2.
> 
> If something inside your tank is creating, breathing out, or injecting more Co2 than naturally found at equilibrium then overly agitating/breaking the water will result in faster gas off.
> 
> If something inside you tank is depleting Co2 faster than might be achieved by natural equilibrium then, said agitation and breaking water will probably result in faster "gas in."
> 
> 
> Fully knowing I could be totally wrong, I shall return the discussion back to y'all, lol. :hihi:
> 
> I suspect the first "if" is more common than the second.


Good point - I agree.

If your plants deplete the co2 levels in the tank faster than they reach equilibrium then agitation should be beneficial. 

I could still debate that you don't want to do it though - at the very least if you have no agitation then for the first few hours of the day your plants will get more co2 - with agitation they will just always get .7...

(I thought it was about 3ppm but I just heard that number from someone else so... yea not very credible) 

Do plant roots obtain co2? 
Lots of bacterial respiration in the soil going on also.


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## Hoppy

It isn't a CO2 solubility question, but a question of the partial pressure in the air and the water being equal. I found a reference for solubility of CO2 in water and it is between .029 and .056 moles per liter. One mole of CO2 is 44 grams, so that is 1.3 to 2.5 grams per liter, which is 1300-2500 ppm! (This is over a temperature range of 20-35C). You can see that this is 100 times the concentrations we use, and 1000 times the equilibrium concentration with CO2 in the air.


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## Hoppy

galabar said:


> First, here is some information:
> Quote:
> However, reguardess of the alkalinity, when CO2 equilibration occurs between water and air the partial pressure of CO2 in the water will equal the partial pressure of CO2 in the air. Assuming that air contains only about 400 ppm of CO2, the concentration of CO2 in water at equilibrium will approach 0.7 ppm ( Rainwater and Thatcher 1960).
> 
> 
> 
> http://www.aslo.org/lo/toc/vol_12/issue_4/0568.pdf


Thank you for that link and information. This is a lot closer to what i measured with water sitting out on my kitchen counter than 3 ppm is. I did some more reading and found a theoretical derivation of that .7 ppm number, giving it a range of .5 to 1.0 ppm, depending on temperature (between 20 and 35C)

Knowing this, it is clear that the belief that if the pH goes up by 1.0 when you degas the tank water, you had 30 ppm in the tank water, is wrong. You had, instead, 5 to 10 ppm, assuming you actually wait long enough for the water to completely degas. This is something I have been insisting is the case for a few years now.


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## Daximus

Chlorophile said:


> Good point - I agree.
> 
> If your plants deplete the co2 levels in the tank faster than they reach equilibrium then agitation should be beneficial.
> 
> I could still debate that you don't want to do it though - at the very least if you have no agitation then for the first few hours of the day your plants will get more co2 - with agitation they will just always get .7...
> 
> (I thought it was about 3ppm but I just heard that number from someone else so... yea not very credible)
> 
> Do plant roots obtain co2?
> Lots of bacterial respiration in the soil going on also.


It's a theory, heck I don't know, lol. One thing I did forget to mention in that post was the bacteria. I figure my canister for about 5 gallons and from what I understand bacteria use up a ton of o2 doing their thing all day...what I don't know is if they put out Co2. I suspect like anything else living and not a plant that they do. Perhaps this is another factor if higher than normal amounts of Co2 in a tank? 

:icon_conf


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## Byron

Now we're getting somewhwere.

Submersed plants are about four times slower at production that the same plant species emersed. This is due to the CO2. CO2 diffuses 10,000 times more slowly in water than in air. The aerial advantage of aquarium plants is well documented and relates to this.

The majority of CO2 in a natural planted tank [meaning no added CO2] occurs from the bacteria in the substrate. Someone asked if bacteria respire: yes. But the breakdown of organics in the aquarium, as in natural waters, accounts for the majority of CO2 in the water, and Walstad cites studies showing that in natural waters this CO2 is used by the aquatic vegetation fairly rapidly. Due to the slow dissolution of CO2 from air into water, it is insufficient as a source of CO2 for plants; the .5 or .7 for instaqnce would never supply anywhere near the amount of CO2 required by aquatic plants. In one natural softwater lake, the pH in the morning was found to be 5.7 and it rose to 9.6 by noon due to the assimilation of the CO2 by vegetation. Photosynthesis decreased sharply from 10am to 12noon, from 16 ug C/l/h to 2.5 ug C/l/h. By late afternoon, photosynthesis dropped further to 0.4 ug C/l/h.

To the question of plant roots assimilating CO2, Walstad says most do not; she mentions the few species of plants that do this, they are Isoetid-type plants like Isoetes, Lobelia dortmanna, etc. Leaf uptake of CO2 is prevalent.

I can't see how this could be different in the aquarium. In other words, the CO2 necessary to drive photosynthesis is only going to occur naturally in the water. And surface movement as Chlorophile said drives CO2 out of the water.


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## dracolique

*I shall test this*

Hello everyone, first post here although I have been lurking for years. I am tired of conjecture, and so I wish to test these things for myself and keep you informed of the results.

I am considering purchasing a meter similar to the one referenced at the bottom of this article:

http://www.microcosmofscience.com/oxyguard_accuracy.php

However, it is only accurate at 1.0 mg/L and above.


In the meantime, here is an interesting post over at barrreport:

http://www.barrreport.com/showthread.php/6418-oxyguard-CO2-meter


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## dracolique

*My test tank*

Notes: Obviously your exact setup will determine your exact needs. For reference, here is the tank I intend to measure:

Extremely Low tech 55 gallon planted:

Un-elevated DSB ranging from 2" to 9" depth

Filtration: DSB, Plants.

Water movement\mechanical filtration: Low-flow, floss-only HOB set low in the water to minimize surface agitation.

Lighting: 2x 40W 2600k 48" strip bulbs. 4x 26W 2600k CFL
Light Cycle: 2 hours of strip-lights only, 8 hours of full-light, 2 hours of strip-only, 12 hours off. 

Tank depth: 18 inches. Distance from surface to lights: 3 inches.

Flora: Tropical Hornwort (Ceratophyllum submersum), Wild celery (Vallisneria americana) , Banana Plant (Nymphoides Aquatica), Java Moss (Wall), Weeping Moss (Bonsai tree - some in the wall as well), and Dwarf Baby Tears (Hemianthus callitrichoides)

Fauna: 7x Tiger barb, 3x Giant Danio, 3x marble Angel, 3 x Otocinclus, 12x(?) ghost shrimp

DSB substrate organisms: California Blackworms & Malayan Trumpet Snails.

CO2 Source(s): DSB, Fish

Algae control: Ottos, MTS, Ghost shrimp

Heat source: Lighting and ambient room temp. Water temp ranges from 68F at night to 74F during the day.

Feeding cycle: one large pinch of flake food every 2 days. Other than that, the fish forage for blackworms, baby ghost shrimp and juvenile MTS. MTS, Ghost shrimp and Blackworm populations seem stable. I also have an electric flying-insect zapper suspended over the tank, which provides occasional food.

Tank maturity (as of this post): 6 months.


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## galabar

dracolique said:


> Notes: Obviously your exact setup will determine your exact needs. For reference, here is the tank I intend to measure:
> 
> Extremely Low tech 55 gallon planted:
> 
> Un-elevated DSB ranging from 2" to 9" depth
> 
> Filtration: DSB, Plants.
> 
> Water movement\mechanical filtration: Low-flow, floss-only HOB set low in the water to minimize surface agitation.
> 
> Lighting: 2x 40W 2600k 48" strip bulbs. 4x 26W 2600k CFL
> Light Cycle: 2 hours of strip-lights only, 8 hours of full-light, 2 hours of strip-only, 12 hours off.
> 
> Tank depth: 18 inches. Distance from surface to lights: 3 inches.
> 
> Flora: Tropical Hornwort (Ceratophyllum submersum), Wild celery (Vallisneria americana) , Banana Plant (Nymphoides Aquatica), Java Moss (Wall), Weeping Moss (Bonsai tree - some in the wall as well), and Dwarf Baby Tears (Hemianthus callitrichoides)
> 
> Fauna: 7x Tiger barb, 3x Giant Danio, 3x marble Angel, 3 x Otocinclus.
> 
> DSB substrate organisms: California Blackworms & Malayan Trumpet Snails.
> 
> CO2 Source(s): DSB, Fish
> 
> Tank maturity (as of this post): 6 months.


I think this will be a very interesting experiment. I wouldn't worry too much about concentrations below 1.0 ppm. We are very interested in seeing if concentrations rise considerably above the 0.7 ppm equilibrium point.

As for the tank, I would suggest switching to a canister filter with a spray bar pointed 45 degrees down. This would causes almost no surface agitation.

This can be significant. I want form two Emperor 280 HOB filters to a single Rena Filstar XP2 canister filter (in a 40 gallon breeder) and reduced my CO2 requirements by 20 times (2 bps to 0.1 bps).


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## dracolique

*Good suggestion*

Your suggestion regarding cannister filtration is a good one. I will make sure to switch over before I actually start experimenting. After good baselines are obtained with the cannister, I will switch back to my HOB and test some more. Be aware, it might take months for me to obtain a good CO2 meter... I need to find a used one, as I am unwilling to pay $1000+ .

However, if at all possible, I will get my hands on one and start testing.


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## galabar

It may be cheaper and easier to simply use a test kit:

http://www.thekrib.com/Plants/CO2/test-kits.html

You could test 1 hour before lights come on and each hour after that until 1 hour after the lights go off.


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## dracolique

galabar said:


> It may be cheaper and easier to simply use a test kit:
> 
> http://www.thekrib.com/Plants/CO2/test-kits.html
> 
> You could test 1 hour before lights come on and each hour after that until 1 hour after the lights go off.


If the meter proves prohibitively expensive, then I may try to find a good test kit, but I would like to obtain very accurate readings. If a test kit is used which proves to be innacurate, then the experiment will do nothing but add to the argument instead of providing useful information.


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## galabar

dracolique said:


> If the meter proves prohibitively expensive, then I may try to find a good test kit, but I would like to obtain very accurate readings. If a test kit is used which proves to be innacurate, then the experiment will do nothing but add to the argument instead of providing useful information.


Good point. It looks like most test kits aren't really any more accurate than pH/KH chart testing.


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## galabar

Another option is to use an accurate pH meter and monitor your pH throughout the day.


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## dracolique

galabar said:


> Good point. It looks like most test kits aren't really any more accurate than pH/KH chart testing.


I think that's because they are, in reality, nothing more than pH test strips. They are just labelled to reflect CO2 conversions instead of pH directly... but as we know, pH is affected by much more than just dissolved CO2.


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## dracolique

galabar said:


> Another option is to use an accurate pH meter and monitor your pH throughout the day.


See my comment about pH being affected by more than just CO2 :smile:

As I said, if the CO2 meter turns out to be simply too expensive, then I may try some of these other things... but first I want to see what I can get my hands on.


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## galabar

dracolique said:


> See my comment about PH being affected by more than just CO2 :smile:


Ah, but the *change* in pH during the day will mostly be the effect of CO2 concentrations.


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## dracolique

galabar said:


> Ah, but the *change* in pH during the day will mostly be the effect of CO2 concentrations.


Not if I urinate in the tank just to make you angry :hihi:

Seriously though, this tank is pretty dynamic.. 

But even if everything was rock-solid stable (which it isn't), I would still need a CO2 meter to
figure out accurately what CO2 concentration is equal to a particular pH reading in this specific tank.


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## Hoppy

It is never sufficient to buy a "good" piece of test equipment, then just use and trust it. No one involved in lab testing, where the results are important, will do that. The other half of the problem with any test device is calibration, and this is usually by far the most difficult half of the problem. I have no idea how any CO2 test device, test kit, or test method could ever be calibrated. That leaves us with using the plants and fish as our test equipment, and testing for "not enough", "about right", and "too much".


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## plantbrain

You can make a known solution of CO2, similar to KNO3 for NO3 stock solutions..........

those 12 gram CO2 cartridges.......can be released and dissolved into a known volume of water.....so you have a weight and a volume of water.......but this needs good seals to prevent loss and a gas lock chamber to measure the samples.

I suppose you could also use frozen CO2, dry ice.........

Melt it in water....etc


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## dracolique

Hoppy said:


> It is never sufficient to buy a "good" piece of test equipment, then just use and trust it. No one involved in lab testing, where the results are important, will do that. The other half of the problem with any test device is calibration, and this is usually by far the most difficult half of the problem. I have no idea how any CO2 test device, test kit, or test method could ever be calibrated. That leaves us with using the plants and fish as our test equipment, and testing for "not enough", "about right", and "too much".


Good points all around. I know from what Tom Barr said in that thread that I linked to earlier, that calibration would be the main problem with this test... and it would be very difficult for anyone else to reliably recreate my exact results, due to tank setup differences and calibration problems.

That being said, however... if this experiment can show the difference between real dissolved CO2 values under different circumstances within the same tank ( different surface agitation levels, different filtration types, CO2 injection, etc), then I think that information would be useful to others in determining the best setup for their situation, even if they do not have the same test equipment.

The calibration does not have to be perfect. It just has to be _consistent _so that the obtained values are all relative to each other and useful in determining efficacious setups.


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## dracolique

*Ah*

Ah, plantbrain == Tom Barr. Nice to meet you 

Here is that link again, in case anyone was looking for it - http://www.barrreport.com/showthread.php/6418-oxyguard-CO2-meter


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## dracolique

plantbrain said:


> You can make a known solution of CO2, similar to KNO3 for NO3 stock solutions..........
> 
> those 12 gram CO2 cartridges.......can be released and dissolved into a known volume of water.....so you have a weight and a volume of water.......but this needs good seals to prevent loss and a gas lock chamber to measure the samples.
> 
> I suppose you could also use frozen CO2, dry ice.........
> 
> Melt it in water....etc


Doing something like those suggestions would result in consistent, if not perfect calibration. And consistency is what is required to make the resulting dataset useful.


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## galabar

I think you may be working with a fairly gross scale. However, if you are seeing something like a 10 ppm rise in the morning, you will be able to see that. Can you tell if the CO2 goes from 0.7 ppm to 0.9 ppm and then to 0.5 ppm? Probably not.


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## dracolique

*True*



galabar said:


> I think you may be working with a fairly gross scale. However, if you are seeing something like a 10 ppm rise in the morning, you will be able to see that. Can you tell if the CO2 goes from 0.7 ppm to 0.9 ppm and then to 0.5 ppm? Probably not.


yes, that is true. No meter I have looked at so far that I have any chance of affording has a finer detection capability than 1 ppm, so it would go up or down by 1 ppm increments.

However, it is these larger movements we are interested in, yes? Who really cares if you are able to get 0.9 instead of 0.7 ppm? a rise/fall of 10+ ppm at various times of the day, and indisputably linked to specific types and amounts of filtration/aeration/turbulence/CO2 Bpm/DSB/Fish & Plant Respiration/etc.; that would be something to take note of.


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## galabar

dracolique said:


> ... Who really cares if you are able to get 0.9 instead of 0.7 ppm? a rise/fall of 10+ ppm at various times of the day, and indisputably linked to specific types and amounts of filtration/aeration/turbulence; that would be something to take note of.


Absolutely! I can't wait for the results. 

--Kevin


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## dracolique

galabar said:


> Absolutely! I can't wait for the results.
> 
> --Kevin


Does that mean I win? I WIN!!!!!!! YAY!!

Now... about that used, cheap meter... 

_**starts randomly cold calling utility workers, water treatment plant inspectors, and research lab associates, and sifting through their trash in the middle of the night**_


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## galabar

dracolique said:


> Does that mean I win? I WIN!!!!!!! YAY!!
> 
> Now... about that used, cheap meter...
> 
> _**starts randomly cold calling utility workers, water treatment plant inspectors, and research lab associates, and sifting through their trash in the middle of the night**_


Unfortunately, no. I already mentioned it here:

http://www.plantedtank.net/forums/low-tech-forum/162480-co2-surface-agitation-2.html#post1715418

in response to this post:

http://www.plantedtank.net/forums/low-tech-forum/162480-co2-surface-agitation.html#post1696302

However, I am happy to have someone volunteer to come along and test previously discussed hypotheses.


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## Hoppy

For slow changes, just tracking the pH would be enough to get an idea about how the concentration of CO2 is changing. And, that is cheap compared to measuring CO2 ppm. You couldn't say how much CO2 you had at any pH, but you could say what the ratios of ppms were, with reasonable accuracy. (10 raised to the power of the change in pH.) Now, the problem becomes one of measuring pH to the nearest .01, which takes a good probe, and calibrations.


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## galabar

Hoppy said:


> For slow changes, just tracking the pH would be enough to get an idea about how the concentration of CO2 is changing. And, that is cheap compared to measuring CO2 ppm. You couldn't say how much CO2 you had at any pH, but you could say what the ratios of ppms were, with reasonable accuracy. (10 raised to the power of the change in pH.) Now, the problem becomes one of measuring pH to the nearest .01, which takes a good probe, and calibrations.


Hmm. If you heavily aerated the tank and causes a lot of surface agitation over a period of time, could you assume that the tank was at 0.7 ppm? Everything else could be based off of that assumption.


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## Hoppy

galabar said:


> Hmm. If you heavily aerated the tank and causes a lot of surface agitation over a period of time, could you assume that the tank was at 0.7 ppm? Everything else could be based off of that assumption.


No, that wouldn't work at all. The 0.7 number has an error range, so it is actually .5 to 1.0. That is about a +/-35% error. Every CO2 concentration number based on that will have at least a +/-35% error built in. So, if you think you have 50 ppm you actually have between 30 and 70 ppm, which is nearly useless information. If you maintain a steady water temperature you can reduce that error, but the .7 number is still a theoretical one, with built in inaccuracy.

However, if you want to know the effect of surface ripple on the CO2 concentration at the midpoint in the tank, just measuring the pH accurately will give you the percentage effect of surface ripple. And, you could determine the linearity of CO2 concentration with bubble rate the same way, or the variation of CO2 concentration over the whole tank volume, etc.


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## Daximus

galabar said:


> Hmm. If you heavily aerated the tank and causes a lot of surface agitation over a period of time, could you assume that the tank was at 0.7 ppm? Everything else could be based off of that assumption.


I think this 0.7 ppm number is derived from Co2 concentration in pure, perfect water. I don't know that that number would ever be actually achievable in a functioning fish tank, what with the bacteria doing their thing and all.


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## dracolique

Considering everything that has been discussed, and the fact that I cannot find any sort of constant CO2 metering system for less than ~$1800 new or used, I think I will likely take the pH approach. A good Ph meter can be had for less than $200.

I do not really like it, because it is an indirect measurement which is potentially complicated by other factors; I wanted something concrete, which could be understood by _*everybody*_, even first-timers and which would indisputably settle the argument. 

However, if the calibration is kept consistent, and the results displayed in clearly labelled, easily understood graphs.. hopefully it will be sufficient.

I will continue for the next 30 days or so to attempt to obtain a CO2 meter, but if it proves completely unworkable, I will compromise and get a Ph meter instead.

Side note: since granular pH meters are comparatively inexpensive, it surprises me that an in-depth study has not already been done by some enthusiast or another. Maybe it has and I am just missing it.


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## dracolique

Does anyone have an experience with the products of Hanna Instruments, Inc.? I am reading mixed reviews on them regarding reliability and accuracy, but it seems that most of the negative reviews are related to long term storage and possible misuse of the device.

Professionals*/*people who read manuals*/*people who take care of their things don't tend to have many complaints.


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## dracolique

*CO2 monitor types.*

You know... decent gaseous CO2 monitors can be had for around the same price as a good pH meter. This is because measuring gaseous CO2 only requires an NDIR sensor, whereas directly measuring dissolved CO2 requires not only an NDIR sensor, but also the added layers of an ATR (attenuated total reflection) optic and a water-impermeable/gas-permeable membrane.

With that in mind, I have been wondering if the following might be possible:

1) use an NDIR sensor to get a good baseline reading for the ambient CO2 concentration in the air (call this variable "*a*")

2) collect a known-volume of water from the tank utilizing a hose to draw water from whatever area of the tank is to be sampled.

3) draw the water into a sealed container of known volume; the sampling hose would be installed into the bottom half of the container. A regular NDIR gaseous CO2 sensor would be installed into the top half, as would a vent-hose. this container would also have a hole in the bottom of it with a rubber stopper. To take a sample, the rubber stopper would first be removed to allow the water to escape during purging of the sampling hose. Once the hose had been purged, the stopper would be replaced, and the actual sample would be drawn into the container by drawing air out of the vent-hose at the top. Once the proper volume was attained, both the sampling and vent hoses would be clamped.

4) The sealed container should then be agitated for a length of time in order to achieve equilibrium between the water sample and the air in the sealed container.

5) Once the sample has been sufficiently agitated, the CO2 concentration of the air in the container can be measured using the gaseous CO2 monitor probe installed in the top 50% of the container. (call this variable "*M*")

6) Perform the very simple calculation of *Result = (M-a)*2 + a* (from the values above) to get an approximation of the total dissolved CO2 in the water sample. This calculation assumes a 1:1 relationship between CO2 concentrations in the air and water when they are at equilibrium, and does not take water quality into account. I shall address water temperature further down this post. 

This calculation does _NOT _ need to take every last variable into account.. the numbers simply need to be relative to each other and variable enough to get meaningful data about CO2 concentrations at any given time. 

Since the resulting values from these tests will be relative values, not necessarily indicative of actual CO2 concentrations, I will not present the numbers as "ppm" or anything else which could be misleading. They should be represented as a relative index, which I have decided to call the *PADCI*; an acronym for *P*lanted *A*quaria *D*issolved *C*O2 *I*ndex.

Most _healthy_ and _established _freshwater planted aquaria have similar base chemistry and exist at temperatures in the 20-30 Celsius (68-86 Farenheit) range, and so likely have similar potential CO2 solubility... but lets look into that:

To determine whether I really need to be incorporating temperature into these tests, lets look at some facts and do some basic math. Looking at the top graph on page 150 of the second below-referenced document, the solubility of CO2 in Freshwater (0% salinity) is *4 Moles/Liter at 20 Celsius* and *3 Moles/Liter at 30 Celsius* (at a pressure of 1 atmosphere).

Henry's constant: CO2 Solubility = (0.034 mol/L * atmospheric pressure)
mass of CO2 = 0.034 moles CO2 x (44.0096 grams CO2/1 mole CO2) = 1.5 grams CO2 per liter.

In other words, 1 "mole" of actual dissolved CO2 is equal to 1.5 grams of CO2 per Liter

So, at a pressure of 1 atmosphere, the total solubility of CO2 in pure, 0% salinity freshwater at 68 degrees Farenheit is 6 grams per liter... and it is 4.5 grams per liter at 86 F.

Almost there... since the readers are mostly American here (I think), lets convert that to gallons:

CO2 Solubility is *22.71 Grams/Gallon at 68 F and 1 atmosphere. (or 3.936%)*

and it is *17.03 grams/Gallon at 86 F and 1 atmoshpere. (or 3.013%)*

I think the disparity is large enough that it should be taken into account... however, I will not incorporate it into the actual PADCI index calculations.. since that method is designed to measure total CO2 content in the supplied volume of water. Instead, since the data will be presented as a relative index, there will simply be a graph showing the hobbyist his/her "Maximum attainable index value" at the temperature of their water. 

So... for now I am calling it good. The calculation to get the index value for any given test will be

*(M-a)*2 + a*

Where: 
*a = the ambient CO2 concentration in the air at the time of the test
M = the Measured CO2 content of the air in the top 50% of the sealed test vessel after agitation. *

And there will be a list of maximum attainable values based on the temperature of your water.


The actual attained values might be different from the REAL dissolved CO2 concentrations in the tank, but at least the numbers will be directly *related *to those concentrations, and so would give a more accurate idea of actual CO2 change over time than pH monitoring.

The actual data will be arranged in such a way that it makes very clear how specific factors affect the index rating of your tank: Including but not limited to: Filtration type, Surface agitation, Aeration, Deep sand beds, Plant types and planting densities, Fish type and number, Feeding schedule, Light schedule, etc.

In other words, I intend to take the guesswork out of planted aquarium keeping when it comes to CO2 and what factors truly affect it.

Obviously I will begin by testing my own equipment and all the different setup variations I can create. Beyond that, the population of the database will depend on how fast I can get new tanks/equipment/plants/livestock to test.

References:

This M.I.T PHD thesis is an enjoyable read, especially chapters 2,3 and 7:

http://www.themckennas.net/uploads/2/6/5/3/2653708/mckennaphdthesis.pdf

This is also good... particularly the graphs on pages 150-154

http://www-naweb.iaea.org/napc/ih/documents/global_cycle/vol I/cht_i_09.pdf


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## FriendsNotFood

It's been a while since this thread started but did this ever get put to rest? I see threads similar to this pop up all the time but I feel like we still don't have a definitive answer for which is higher, atmospheric CO2 or the CO2 in the water?


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## PlantedGuest

*subbing* I am very interested in this topic. . .


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## pandamonium

im also really interested in this topic since i may be adding a air pump to my tank based on the CO2 conditions being discussed if its better to aerate or not due to CO2 solubility.
what i wonder is we have already established some amount for levels of CO2 in the water (0.7ppm or something along those lines). if plants use this CO2 which would reduce the concentration, wouldnt equilibration with atmospheric CO2 cause the levels to stay somewhat constant at 0.7ppm with minor fluctuation (Lechatelier's principle)?


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## galabar

pandamonium said:


> im also really interested in this topic since i may be adding a air pump to my tank based on the CO2 conditions being discussed if its better to aerate or not due to CO2 solubility.
> what i wonder is we have already established some amount for levels of CO2 in the water (0.7ppm or something along those lines). if plants use this CO2 which would reduce the concentration, wouldnt equilibration with atmospheric CO2 cause the levels to stay somewhat constant at 0.7ppm with minor fluctuation (Lechatelier's principle)?


The aeration *may* remove CO2 that is being generated from decay within the tank.


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## pandamonium

galabar said:


> The aeration *may* remove CO2 that is being generated from decay within the tank.


oh i see and that CO2 from decay is desirable in planted tanks then


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## FriendsNotFood

That's what we're trying to find out, if CO2 from decay/fish breathing within the tank is greater than atmospheric concentrations.


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## kalawai2000

FriendsNotFood said:


> That's what we're trying to find out, if CO2 from decay/fish breathing within the tank is greater than atmospheric concentrations.


I'm really enjoying this thread and topic.

I have some surface agitation while running a powerhead with quick filter and a canister filter that sits low under the surface..
At night I run a Hydor Bubble maker... my C02 drop checker is always green or a light green.

My tank does have a fair number of fish and I don't always grab out dead leaves
anyway, I really never think about C02 as long as my plants and fish are thriving in my tank.


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## Django

FYI, The concentration of *carbon dioxide (CO2) in Earth's atmosphere* is approximately 392 ppm (parts per million) by volume as of 2011
- Wikipedia (see links)


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## Complexity

Django said:


> FYI, The concentration of *carbon dioxide (CO2) in Earth's atmosphere* is approximately 392 ppm (parts per million) by volume as of 2011
> - Wikipedia (see links)


Might be true, however, Wikipedia isn't the best resource to use. It's best to look for an .edu resource (preferably one from a university).


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## m8e

Complexity said:


> Might be true, however, Wikipedia isn't the best resource to use. It's best to look for an .edu resource (preferably one from a university).


Just look at the reference.


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## Django

fish h20 said:


> I googled CO2 in the atmosphere and it is 390 PPM. We should all get airstones for our aquariums! Someone with not enough information is just as dangerous as someone with none.:icon_wink


I can confirm googling CO2 in the atmosphere as 390.


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## Squatchmen

fish h20 said:


> I googled CO2 in the atmosphere and it is 390 PPM. We should all get airstones for our aquariums! Someone with not enough information is just as dangerous as someone with none.:icon_wink


So does that mean we can have water agitation or not? That probably means yes, we can have agitation


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## Luminescent

I have two powerheads in my 40- pretty good flow. I have one (facing the front glass from back right corner) facing down. The bigger one is in the same back corner facing the opposite wall- far end. Its flow is directed toward the surface. It's deep because I have it upside down with a pond sponge on it. It 'roils' the water at the surface. I use diy CO2 4 hours of the day- peak lighting time.

Everything is a-ok so far.


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## galabar

Squatchmen said:


> So does that mean we can have water agitation or not? That probably means yes, we can have agitation


For well aerated water, the carbon dioxide concentration will be less them 10 ppm.


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## plantbrain

galabar said:


> For well aerated water, the carbon dioxide concentration will be less them 10 ppm.


Closer to 1-2 ppm. 

Put another way, folks are confusing gas ppm's and water ppm's. 
They are not equivalent. Far from it.

Dissolved gases have different solubilities in water(eg, O2 and CO2) and there's only so much dissolved gas water will hold at equilibrium(it's mostly water, not gas). Any more than equilibrium is then governed by Fick's 1st law of diffusion going from a higher concentration(in this case, the water) to the air above. The higher concentrational difference between the water and the air above, the faster the flux will be. This is not a linear relationship either.

Degassing is rapid initially, then tapers off in a decaying exponential curve. The same is true in reverse, when you try and add more and more CO2, it is fast initially, but then becomes much harder as the concentrational difference becomes higher.

Now if you had a sealed aquarium, okay, but we do not have a sealed aquarium, we have a lot of nice clean thin layers of water with large surface area. Adding ripples or movement will also make this harder to maintain a concetrational difference, and the flux will increase.

So higher concentration and more surface area/turnover etc= higher flux rates. But...we get nice O2 levels with surface rippling, there are other gases involved we like, and we can add more CO2 without too much issue.
Yes, we lose some CO2, but we gain more O2 and clean tanks.
You could dose pure O2, but..........it's more toxic than CO2 relatively speaking.


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## Django

I hope I didn't miss any messages pertaining to what I'm about to say, but here goes - I appreciate learning about partial pressure atmospheric and partial pressure (dissolved in water).

I am talking about non-injected CO2 tanks. I think that any disruption of the water surface at any time will result in less dissolved CO2. It increases gas exchange at the surface to more than the default. Breaking down of organics in an aerobic situation results in CO2 - all the time. There is a chart which shows how much CO2 you have in your tank at a certain pH and KH. Also, as the temperature goes higher it results in less dissolved gases.

I personally don't think it makes sense to turn on a bubbler in the afternoon when the plants have stopped photosynthesizing.

Aside from surface water movement that disturbes the water surface, movement under the surface that moves water and its gases and nutrients around the tank and to the plants and minimizes "dead spots" is very important. Hope this is useful for perspective and background.


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## fishnoob

I am currently injecting CO2 in my tank. Should I turn off my HOB filter during the day? I've accidentally turned it off before, and my stock almost died had I come home minutes later(this happened before I had CO2 injection).


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## Django

fishnoob said:


> I am currently injecting CO2 in my tank. Should I turn off my HOB filter during the day? I've accidentally turned it off before, and my stock almost died had I come home minutes later(this happened before I had CO2 injection).


What HOB is it? What's the manufacuter's rated throughput in gallons per hour. What is your stock?

Movement of the water throughout the tank is the most important thing because it exposes oxygen-poor water to oxygen-not-as-poor at the tank surface where the oxygen enters the tank. A Wet-dry filter would be a fantastic thing because of all the surfaces exposed to air and tank water. But even then, tank circulation cannot be ignored. I like the looks of the Hydor Korelian powerhead. It's not your father's powerhead anymore.

The big question is what fish do you have (please list). If you are overstocked, re-home some fish. If you get a Koralian or some other powerhead, you could leave it on all the time. 

Of course, with good tank circulation comes increased gas exchange at the surface. I don't know how much CO2 would be lost - best ask someone with a CO2 system. You could ask them as well about CO2 vs. O in the tank. I dont have a CO2 tank but I don't think as long as the CO2 supply is under 30ppm the inhabitants are safe.


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## ZeeDeveel

What about holding air in your lungs for a while then blowing into the tank through a big straw / pipe repeatedly? Would that help at all?


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## MikeyDTan

*Just a thought*

Old thread but love it. Learnt a lot from everyone 

Just a thought though ... we have bunch of buceps and other plants in our tank that grows both emergent as well as immersed. Notice that such plants grows better in the air. From earlier posts i guess this is from air being better able to diffuse CO2 efficiently for the plants' use.

So should it follow that in a tank without CO2 being pumped in, water being helped by agitation to come to the same equilibrium as the composition of air should ultimately prove to be beneficial (in the sense that they should grow no less worse than growing emerged in air)?


----------

