my smallest tank is my 75. i use an emperor 400 which has never failed me yet and keeps my tank clean. i have had bad experiences with canister filters in the past, more specifically fluval 404's and i will never use a canister filter again. a lot of people i have talked to have problems with them leaking, maybe not all, but i know of a thread a while ago with which people had the same problem. not to mention you better have that hose that dumps the water back into the tank anchored properly and securely because if not they will pop out and filter the water all over the floor until the tank is empty. i've had this happen to me when i first started and lost all but 5 gallons in my tank.