# overdosing CO2?



## Aaron (Feb 12, 2004)

Here's something I've always wondered, but never really pursued an answer. What are the ramifications of overdosing CO2? I know that fish and shrimp et al can die, but what are the limits regarding plants? Is it a ph issue? I know the reccomended amount of CO2 is 30ppm, why? How far away is this to saturation? If this has been covered in the past, does anyone have a link to the thread? I'm too lazy to go and blindly look.


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## Edward (May 25, 2004)

Hi

There seems to be no toxicity level to the plants. I grow plants in pH of 4.0 and also in CO2 concentrations of 300 ppm. More CO2 won’t push pH any lower than that so the value becomes stable. I do not see any benefits from running the CO2 that high. The plants look the same.
There are posts about research, where was proven that CO2 levels over 30 ppm make no difference in plant growth regardless the amount of light applied.

Edward


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## cS (Jan 27, 2004)

Maximum saturation of CO2 in water is not an easy number to calculate since it is dependent on so many variables (pH, pressure, temperature, other solutes, etc.).

Aaron, I hope that you don't mind if I annex the thread a bit here. :mrgreen: Edward, how can you sustain 300 ppm CO2 when your tank is virtually devoid of carbonates? Moreover, how can it not exhibit a pH-crash? Even if a pH-crash is not possible, does the fauna not die from too much CO2 even if there's plenty of O2 around? I am thinking 300 ppm CO2 is enough to affect the diffusion of CO2 out of a fish's body. Or is 300 just sound big to me?

I've always been told that CO3 is vital to protect the pH from changing too drastically, thus killing the fauna. If this is not true (and I would like to know why, if possible), then it would save me a lot of trouble. I currently dose CaCO3 as a source of both Ca and CO3. I wouldn't mind switching to CaCl2 since it doesn't cloud the water for several hours like CaCO3 does.

Thanks much.


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## Aaron (Feb 12, 2004)

Hmmm, very interesting. So would it be safe to say that an excess of CO2 does not directly affect the plant's needs in terms of ferts and light after 30ppm? 

What about algae? It is preached here that a consistent level (30ppm) of CO2 (along with providing ferts in correct proportions...) will go a long way in keeping algae at bay. Is algae affected by excess CO2?

Cs, annex away! I too want to know about bottoming out the Ph and keeping it stable. Also if fish are okay swimming in 300ppm of CO2. Perhaps it could be another way to keep ph low enough to breed certain fish(?)


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## chiahead (Dec 18, 2004)

If I remeber Edwards high Co2 tank is fish free. and yes that much Co2 will definetly kill all fauna. I run 30-40 and there ok but when my Co2 reaches around 50 ppm the fish gasp at the surface. Not from lack of O2 just excess Co2.


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