Can CO2 injection be used with under gravel filters?
Certainly! What you don’t want to use, however, are airstones to drive the UGF — powerheads are the preferred method. The turbulence caused by the bubbles on the surface will greatly increase the rate at which CO2 diffuses into the atmosphere. In general, an aquarium with CO2 injection should not have a lot of surface turbulence. Likewise, if your canister filter has a “spray bar”, move it under water and point it towards the bottom to avoid a lot of turbulence. The “water fall” return from various power filters will not cause much loss of CO2.
