# CO2 Reactor Discussion - Personal conclusions re: Foam and Bioballs



## anonapersona (Oct 19, 2002)

*stopping fish*

The sponge on the Plantguild reactor also keeps fish from getting into the reactor where the CO2 level might be too high for safety.

I note that with a slightly longer tube and a lower flow, like the Rio50 the plantguild uses, the bubbles would never escape the bottom. I have a DIY version of the plantguild one, and an original. I used a Rio90 and it is a bit too strong, a 50 would be better, it does not take much flow to churn those bubbles. If you have high flow, you need the end sponge and the bioballs to try to make it all mix.


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## BlueRam (Sep 21, 2004)

unirdna said:


> So why, when I look at online photos of manufactured reactors, did they have so much gas bubbling in them. The answer: That gas is NOT CO2. I can't tell you what it is (Nitrogen, Oxygen, Argon, or a combination I suspect), but I can say with confidence that it is not CO2.


In DIY I would suspect air from the initial sealing followed by mostly CO2 plus all the other stuff yeast produce. If infected with bacteria I assume you could add methane etc...

Since you are using pressurized I would suspect that you could get that information on the bottle or from the supplier. Would you be kind enough to post your source/grade so we could compare? Could you also include pH/KH/projected CO2 to see how soluble CO2 is in your system?


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## Rolo (Dec 10, 2003)

Very nice observations and summary. 

But I really don't know how you came to conclude that the tiny bubbles churning a long time in the reactor is not CO2. The only gas injected into the reactor to begin with was CO2. Pressurized CO2 should not be any less then 99.9% pure.

Here's my take. I've watched a glass/ceramic diffuser in action that puts out very tiny bubbles - but there is some variation in size. The largest the the bubbles rise very fast but in no time, literally less then a second, it decreases size and slows down to a very slow speed. But the smallest of the bubbles come out at the same speed and size and there is no noticeable decrease in size or difference until it hits the surface.

What I'm trying to illustrate is as bubbles get smaller, the rate of diffusion also decreases - so much so that any further dissolving isn't noticeable. So all those tiny bubbles are still CO2. 

Just my 2 cents.


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## unirdna (Jan 22, 2004)

Interesting observations.

anonapersona,
I tested the unsafe-for-fish hypothesis. I inserted a 5ml syringe into the bottom of the reactor. The intake (of the syringe) was about 1 cm from the top (water outflow and CO2 injection). Initial pH readings indicated a .02 difference between the water in the reactor and tank water (6.74 vs. 6.72 in my case). I tested twice more and the results were the same. If there was a build up of CO2 in the reactor, I would imagine that the pH would be significantly lower. This further reinforces my belief that the "stubborn" bubbles are not CO2.

Blueram,
Thanks for contributing re: DIY CO2, as I have no experience.  The pressurized CO2 that I am using is the same stuff sold at welding supply stores. Here is a photo of the label.










At the time I performed the "gas rush" these were my water parameters.
pH 6.74
KH 5
GH 5
CO2 injection 60 bmp

Rolo,
I can't say what the gas is, as I stated. But if you read about my experiment, you'll see that it would make no sense for 95-99% of the CO2 I injected to dissolve within 2-3 seconds, and then, for no unknown reason, have 1-5% CO2 simply "decide" not to dissolve with the rest. Do you see what I'm saying? If the reactor can dissove 95% of the injected gas within 2 seconds, what would stop if from dissolving all of it....unless, that gas was NOT CO2.

You also said, "What I'm trying to illustrate is as bubbles get smaller, the rate of diffusion also decreases - so much so that any further dissolving isn't noticeable. So all those tiny bubbles are still CO2." 

I would diagree with this. First off, smaller bubbles have a higher surface to volume ratio. Meaning that they have more gas in contact with the water, with respect to their volume. Meaning, they should dissolve faster. What would stop a tiny bubble of CO2 from dissolving? What I would suggest is that those tiny bubbles you are seeing are the remants of a once larger bubble of gas. That larger bubble consisted of 95-99% CO2, all of which dissolved quickly, leaving a tiny, hard-to-dissolve bubble of some other gas (Oxygen? Nitrogen? etc). 

I don't know how soluble Nitrogen or Argon are in water, but I do know that Oxygen is NOT very soluble. 10-12 ppm is full saturation. Whereas CO2 can be dissolved into the hundreds of ppm....maybe thousands. This saturation of oxygen is why plants can "pearl" oxygen during the day. Additionally, the easy at which CO2 dissolves may help to explain why we never see our plants "pearl" CO2 at night.


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## baj (Sep 16, 2004)

unirdna said:


> I don't know how soluble Nitrogen or Argon are in water, but I do know that Oxygen is NOT very soluble. 10-12 ppm is full saturation. Whereas CO2 can be dissolved into the hundreds of ppm....maybe thousands. This saturation of oxygen is why plants can "pearl" oxygen during the day. Additionally, the easy at which CO2 dissolves may help to explain why we never see our plants "pearl" CO2 at night.


 if I had a fishless tank I would continue to saturate the water with co2 with the lights off to see if at any point co2 is saturated to the point that it does not dissolve anymore and bubbles to the surface from the leaves. But I think you are right, in the short amount of time that the lights are off and the plants are respiring, co2 saturation may not reach that high a level. Also, i agree to your thoughts on the sponge/bioball stuff, the sponge prevents bubbles from coming out but if the chamber is placed right (ie vertical) the amount of bubbles coming out would be very less, the sponge tends to slime up and clog and push water into the co2 tube which for a DIYer is very annoying (since you would tend to believe the batch has died and you need to refresh it). The bioballs are also superfluous, there is no need to "break" the bubbles by turbulence, the water flowing into the chamber is enough to induce the chaotic movement of water inside to induce dissolution.


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## TeeItUp (Mar 18, 2004)

That’s why I now love my Eheim CO2 diffuser. Been there done that with the internals and externals (much better then internal). It drove me crazy the accumulation in the chamber. I also have the same observations that Rolo had using this diffuser. Some of the larger bubbles fly up so fast and before they reach the half way point they are a fraction of their size and slow down incredibly. 

Unirdna I have never researched this but I doubt that welding gas CO2 is pure CO2 which is what I think Rolo meant.


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## anonapersona (Oct 19, 2002)

*Breaking OUT of solution*

First, good work in testing the hypothesis on high CO2 levels inside the reactor! I like facts better than half-baked theories anytime, even my own half baked theories.

The gas in the churning CO2 reactor may actually be oxygen that is being broken out of solution. I know that a pump that is working too hard can cavitate and pull gas out of solution, so in a well saturated planted tank, taht is probably the case. I recall some long discussions of that here or somewhere at one point.

For the DIY CO2, there will be a fair amount of air that is not CO2 in a bottle at start up and so bubbles ought to have a portion that is not absorbed. That portion ought to get smaller as time goes on. 

Lastly, since the volume of a sphere varies as the cube of the diameter, as long as you see substantial reduction in diameter, you have very good absorbtion. If the diameter is reduced to 25% the original diameter, the volume is reduced by 98.5% -- not too bad, IMO. So, don't sweat the small remainder, particularly on DIY at the startup.


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## unirdna (Jan 22, 2004)

Very good point re: the volume of a sphere. This shows that it really doesn't take much gas to make a bubble, meaning that even if the CO2 gas in the cylinder were 99.9% CO2, you would still see plenty of undissolved gas - especially if the tank was already saturated with O2.

Re: Oxygen coming out of solution - I think you are right on. By the end of the day, my plants are bubbling like crazy, there are small bubbles circulating all over the tank, and the reactor is FULL of bubbles. By the next morning, all these bubbles are gone, and the reactor is clear.

All these findings continue to reinforce the original statement (although, if they didn't, I wouldn't be too stuborn to admit my error)....bioballs and foam are not needed .

Furthermore, the speed at which we've described CO2 to dissolve, illustrates how effective a diffuser can be. Even though, small bubbles are seen reaching the surface, there is a more-than-good chance that those tiny bubbles are NOT CO2 (eg. diffusers are just as capable as reactors).


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## DennisSingh (Nov 8, 2004)

This may seem stupid, or really obvious, or maybe it was already said, or what am I talking about, whatever. Sorry, but I think the gas is o2 because its co2 and the C gets dissolved and what you already injected co2 the o2 is left which is already at full saturation, I think. And with that, you are left with those remainder bubbles that kind've get on your nerves because they never shrink down, or it seems they never do.


Denny S.


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## Wasserpest (Jun 12, 2003)

I am pretty sure it is Oxygen. That's based on the observation that "air" seems to build up in the afternoons, while in the mornings it's gone, or mainly quickly dissolving CO2. As O2 saturation is reached, any airspaces seem to attract the pearling O2. Not only CO2 reactors, also my Filstars seem to collect some air in the afternoons which the noisily spit out. In the mornings, things are quieter.

Anyway... I absolutely agree that it is better to skip spongies and bio-balls.

Strungout: I don't think CO2 splits up into C and O2... rather it dissolves in water and turns into carbonic acid.


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## unirdna (Jan 22, 2004)

Wasserpest said:


> I don't think CO2 splits up into C and O2... rather it dissolves in water and turns into carbonic acid.


This is exactly right. The bond between the Carbon and the two Oxygen atoms is covalent; a very strong bond. Gases and solids dissolve in water because of polar bonds. These are comparitively very weak. Water, as we know, consists of H20. When you add CO2, you get molecules of H2CO3 (carbonic acid). The formation of this weak acid is what lowers the pH. 

Have you ever popped open a can of soda right under your nose? Did you feel that tingly, stinging sensation? The burst of CO2 from the soda reacted with the water in your nose and eyes and formed Carbonic Acid. It's quickly diluted and the feeling goes away.


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## Aulonochromis (Jan 14, 2005)

I am experiencing the same thing with yeast generated co2. I get a buildup of gas in the top of my DIY reactor. When I purge this gas out, I can watch the new bubbles rise up and dissolve within about 10 seconds. But over the course of a few hours, the gas builds up in the top and it doesn't seem to dissolve at all. I am using some lava rocks in my reactor and I thought bioballs might be a better solution, but maybe I should not use anything in there?


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## jstehman (Dec 13, 2010)

What an interesting thread... This subject has been bugging me ever since I set up my reactor. 

Whatever those bubbles are, my Gouramis sure like to slurp them up!


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