Too much CO2?

James0816

James0816

AC Members
Feb 14, 2007
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This may have been asked before but I don't recall reading it. Is it possible to OD on CO2?

Here's why I ask. I have a DIY jello mix getting ready and was going to put in on a 20long tank that currently is using the regular mix. So...in the event that it actually works...then I will have two 2L bottles producing CO2.

The tank that it will be on currently is housing "jaws" my mystery appearing cherry barb and some ghost shrimps.

thx
 
2 bottle on a 20L might be a bit much. I have 2 regulars on my 35 but I don't have a good diffuser right now and the tank is high light and chock full of planty goodness.

Too much CO2 will cause pH swings, depending on your hardness, and can 'suffocate' your inhabitants. Your plant load and diffusion method will factor into how much there is dissolved in your aquarium.
 
Yes. Anything more than 40-50ppm can be harmful or fatal for your fish. Most people aim for 20-30ppm. Keep in mind that DIY CO2 probably will never see those levels, however. (depending on how well the CO2 is being diffused into the water, of course.)

I'd test your water if you're concerned about the levels being too high.
 
Absolutely! Excess CO2 can lead to suffocation of specimens. A very precise gradient between O2 and CO2 must exist for fish to respire.

One way to objectively measure the levels of CO2 in the tank is to use a drop checker filled with 4dKH fluid and a few drops of bromophenol blue pH indicator fluid. It just so happens that this fluid will change color to help target a CO2 concentration of 30ppm, which is great for plants and not dangerous for fish.

blue color = not enough CO2 in tank

green color = good CO2 levels (~30ppm)

yellow to orange = too much CO2 (danger)
 
What happens is fish excrete CO2 by diffusion. The ease with which this occurs depends on the difference between the blood CO2 concentration and that in the water - called the diffusion gradient. As water CO2 concentration rises, the gap narrows and the gradient is reduced, so the efficiency of CO2 excretion decreases, ultimately to a point where the fish can no longer excrete enough CO2 to take on sufficient oxygen in its place. CO2 does not expel oxygen, but prevents fish from taking it on by keeping CO2 in the blood.
 
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