yep, the extra CO2 pushes oxygen out of the water (and the fishes' blood), and anesthetizes them. they usually turn upside-down, like they're about to die. so it's a very delicate balance: you want them out, but not so bad that they can't recover. while they're under, we'll put a tube of fresh source water into their mouth, so they get oxygen and don't suffocate. that alone is enough to let some fishes recover, so we have to put them back in the CO2 tank. they recover fully pretty quickly as soon as they're back in regular oxygenated water.
