Join Date: Oct 2006
Location: Leesburg Virginia
It sounds like you are using a Hang on back filter like an Aquar Clear or Whisper. There would be some lose of CO2 if injected into the filter. But, it has been done before so you might still get some benefit. Just make sure your lighting isn't too intense or you might have algae problems.
I just noticed your post indicating 2xT5HO. That is probably too much light for yeast based CO2. You might see if you can run that light with one bulb. Usually not but, it's worth a try.