" wrote:


This is really interesting. In between my last post and this, I was up at a fish
store that told me about a fish die-off they attributed to not turning off the CO2 at
night. I looked at their tank: needle valve, no cover, lights suspended 8 inches
above the tank, no chance of CO2 being trapped above the water and displacing O2.

That would not occur anyway.

Tom,

I'm sure we've both seen the case where a tightly fitting hood on a CO2 injected tank
caused CO2 buildup. The outgassing CO2 gets trapped in the enclosed air space above the
water, and prevents sufficient O2 from diffusing in. The common solutions are to open air
gaps in the hood or install airstones.

It happened he

http://www.tactics.com/d/svas/sam.html

The tank on the left is CO2 injected. The hood is tightly sealed. An airstone solved the
problem. The tank on the right is not CO2 injected, and did not have problems.