If you have extra air going into the filter check all your intake pipework. I had a problem with one of mine (I have 7 of these aps filters I love them). Make sure the hose is fully pushed up to the line on the black u shaped piece. Try removing it and using a dab of vasaline all around the end of the pipe and re fit the hose (its not harmful to the fish) if its still sucking in air you may have a pinhole in the black u-shaped piece. Where the intake pipe joins to the u shaped piece is this under water? sometimes if its above and the intake pipework is not pushed up as far as it will go, sometimes air will get sucked in there. Try all this first then e-mail APS explaining what you have tried, they should send you a new u piece if it is that sucking in air.