How much CO2 is too much? - The Planted Tank Forum
 
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post #1 of 10 (permalink) Old 02-14-2005, 03:30 AM Thread Starter
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How much CO2 is too much?

CO2 concentration in water shouldn't effect O2 concentration, does it?

Let's say that if I do not want to use chemical means to lower my pH, and want to rely solely on CO2 to keep my water slightly acidic. My present tap pH is 7.6, KH 4, and if I keep dumping CO2 into water to drop the pH till it stablizes at 6.8. Would too much CO2 in the water kill my fish by blood acidosis?

Is acidosis only occur when pH of the water falls significantly below 6? What would happen to planted tank if you have too much CO2? Is pH drop the down side to have too much CO2 in the tank?
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post #2 of 10 (permalink) Old 02-14-2005, 04:17 AM
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I think too much CO2 would kill them by displacing the oxygen they need to breathe. You'll see them at the top of tank trying to get air. A Kh of 4 with a Ph of 6.8 will give you approx. 19 ppm of CO2. I don't think you would start having real problems until your Ph lowered passed 6.6 or so.


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post #3 of 10 (permalink) Old 02-14-2005, 04:27 AM Thread Starter
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But isn't CO2 and O2 each independent in water? For example, when you have more CO2, does that means you would have less O2?
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post #4 of 10 (permalink) Old 02-14-2005, 04:39 AM
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I couldn't really answer that without doing some research. I have only read about too much CO2 in the water will not allow the fish to breathe. I know that if you open a CO2 canister in a closed room, it won't be long before your in trouble.


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post #5 of 10 (permalink) Old 02-14-2005, 04:44 AM
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This may help - http://www.thekrib.com/Plants/CO2/poison.html


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post #6 of 10 (permalink) Old 02-14-2005, 02:06 PM
 
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Too much CO2 does not reduce the O2 concentration. Too much CO2 in the water makes it harder for fish gills to flush CO2 out of the fish's blood since the CO2 concentrations get too similar.

According to the charts, I've had CO2 up to 60mg/l with no visible effects on the fish...
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post #7 of 10 (permalink) Old 02-14-2005, 02:17 PM Thread Starter
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Quote:
Originally Posted by Laith
Too much CO2 does not reduce the O2 concentration. Too much CO2 in the water makes it harder for fish gills to flush CO2 out of the fish's blood since the CO2 concentrations get too similar.

According to the charts, I've had CO2 up to 60mg/l with no visible effects on the fish...
Yay! Thank you. That surely explains the mystery.

But if 60ppm has no visible effects, then up to how much should I be worried?

BTW, How is CO2 and KH relate to each other in our aquarium? What effect does CO2 have on KH when we increase CO2 to the water, assuming everything else unchanged?
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post #8 of 10 (permalink) Old 02-14-2005, 02:57 PM
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You only have about 20ppm at 6.8 pH. If you are injecting CO2 for a planted tank, your target should be 6.6 pH. We calculate the CO2 concentration through a formula using KH and pH readings. Plants can't use more than 30ppm, but there are a number of folks who keep levels around 40ppm and none of the fauna are affected. Mostly, the O2 level is supersaturated in a planted tank with 30ppm during the photoperiod because of photosynthesis. That's what pearling is all about- outgassing of the O2 in an injected tank. So, yes, in planted tanks CO2 level does affect O2 concentration during the photoperiod by increasing it. But CO2 concentration itself does not displace O2.

Chuck's calculator saves you having to do the math when calculating your CO2 level.

James
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post #9 of 10 (permalink) Old 02-14-2005, 04:55 PM
 
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so pealing is a sign of a tank in balance or just co2 in balance?

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post #10 of 10 (permalink) Old 02-14-2005, 05:12 PM
 
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pearling only indicates that you have full oxygen saturation, so the O2 the plants give off has to bubble to the surface. My 75gallon would pearl if I didn't keep so many fish in there, which prevents full O2 saturation.

People will run CO2 a little over 25ppm because they feel it helps combat algae problems, and that certain plants in particular can and will use higher CO2 levels effectively.
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