A specific question...

[Jasonator]

In a heavily planted tank with fish, what effect would a co2 diffuser have on the fish?

[gklaw]

Nothing really unless you pump a whole ton and drop the pH too much.

[2wheelsx2]

Nothing really unless you pump a whole ton and drop the pH too much.

or if you pump a whole ton and poison your fish with toxic levels of CO2. CO2 pH swings are transitory but CO2 poisoning is not.

[Jasonator]

I didn't figure a moderate amount would be harmful.

Good affirmation, folks.
Thanks