I am looking for suggestions on a particular issue I am having with my Fluval 405 canister filter. I have a (now) lightly stocked planted 75 gallon freshwater tank. Over time, the canister seems to develop air pockets in it. As a result, the gph
seems to be affected. If I rock the canister around, I will get the "churn" sound it makes as it processes air through it.
I thought perhaps my tubing configuration might be the problem. The 405's output goes through a Turbo-Twist 12x-36 UV
sterilizer before returning to the aquarium. I had the sterilizer mounted horizontally so that the 405's output went straight up into it, then on the other end it went out of the side before going back up.
I thought maybe the air was getting trapped in the sterilizer, so I moved things around so that it would be vertical and the flow would travel bottom to top. To do this, the 405's output goes back down to near the bottom of the canister into the sterlizer, where it then travels straight up through it and back into the aquarium.
Now I am positive the sterilizer is no longer the reason air is getting trapped, but the canister still
develops air within it. I am convinced the gas is the toxic byproduct of the nitrogen cycle happening within the canister, because since this problem has started happening I have had massive fish deaths.
My last option seems to be to move the UV
sterilizer one more time so that at no point does the water have to travel back down before going up again. It is just I am hard-pressed to believe that the 405 does not have enough power behind it that this problem should be occurring in the first place, but that seems to be a logical deduction.
The 405 contains only the filter pads and all the trays are stocked with bio-rings; no carbon.
Does anyone have any more thoughts before I dig into this once again?