I have a 75 gallon tank with decent filtration (2 Emp 400s a power head with filter & a Fluval 404) But I am a little concerned about one thing. I have a air line attached to this fairly large power head in order to increase oxygen in the tank, the problem is that the Fluval 404 sucks up a lot of air and every 25 minutes or so I can hear it purge trapped air back into the tank. There is always air trapped in it. Even after it burps out trapped air I will kneel down and give it a little shake and a whole lot more trapped air comes out. This has become somewhat frustrating considering I have to do this at least 5-6 times a day. I remove the canister every other week to clean off the foam so I know it is clean. Is the air that comes out toxic though, after being trapped inside the canister for a half an hour to an hour and a half? I have tried moving the canisterâ€™s intake line all over the tank and it still sucks up air. :?