My pump is shooting out micro bubbles back into my tank, its a 1.5" return that it uses. What if I get a 3" tall section of 4" pipe then put a small section of filter floss in the 4" section, I would use brushing to get it back to 1/5 on both sides. So basically the 4" would act like a ghetto in line filter. My tank looks dirty when its actually really clean.