Sponges seem to be a Nitrate factory, What i do with my aquaclear is run it as a fuge, I didnt notice if your tank was a reef tank or not. But a having some kind of plant or algea in your tank that consumes nitrates will help keep them low or at 0. On my 55 gallon I dont run any filtration except for the AC70 empty except with some chaeto macro algae in it my nitrates stay at 0. I use RO
water for top offs and PWCs (with salt for pwc
's obviously). Just my .02 if you want to give it a go i have a ton of macro that i could trim for you and ship if you want to pay shipping.