I have what might seem to be an unusual setup. I have a homemade stand that supports my 75 gallon tank. When we built it, the thought was to put a canister filter on the bottom shelf, which we did until it died. We then got the bright idea to put my 29 gallon tank on that shelf. The 75 runs 2 Aquaclear 110's which I am very pleased with. I am running an Aquaclear 70 on the 29, Now on to my question. Is there a canister filter (perhaps a Sun Sun) that I can run on the 29? I've heard that most canisters use gravity to operate. Because the shelf the 29 sits on is only 6 inches above the floor, would this even be something to consider?