i run a single fx-5, with a sponge on my 400 gallon with over 60 fish in it. i do run 2 300 watt heaters. one day i plan to drill another hole to add a second canister, weather its a fx-5 or eheim filter. know my 150 open top has 3 110s and 2 305s on it because it open, if i waas more patient i would have drilled more holes in the 400 before i set it up. like you never used a sump, and it wasnt going to be on this tank.