Ok guys I need to know what you all do. When you get a filter do you go for the ones that are made for your size of tank? When I got my HOB aquaclear I got it 'cus it was made for the size of my tank. Is this approach really necessary? It's a very heavily planted tank with CO2 but as long as the surface is agitated, Im alright....righT? I'm asking because I wanted to get a fixture from AHsupply, I dont really seem to have enough room on top. You see my tank doesnt have a cover, its just open....i've got a filter thats rated for a 20gallon wold this suffice for my 40gallon breeder tank?