it's overkill, but I run an eheim 2213 on my 20gallon, which has about 16 gallons of water in it. I like it because it's truely silent, has a great flow rate, and because I can route the intake and return where I want them in the tank, rather than next to each other like an HOB. to me, it was well worth the added expense. If I could, I would always use a canister.