This, in this order.
Bottom: coarse filter media ( pad with the unit will work fine)
Middle: fine filter media ( Use what came with it ) polyfil is very nice as well.
Top: Bio media ( Seachem matrix or equivilant ).
I bought a CF400 to see how it stacked up against the Marineland c360 (The filters sold by Aquaclear are Marineland knockoffs). It wasn't a bad unit. However, the Cf400 felt very thin and cheap compared to the Marineland. The valve block on the cf400 was very fragile ( Boil some water and soak the end of the hose before installing or you may crack the valve block. I did not compare gph
, I just felt the pressure coming from the outlets, the Marineland seemed a bit stronger.
I have heard good things about these units though. Make sure you keep the seals lubed with silicone grease or vaseline. This seems to be the secret to keeping just about all canister filters sealed and leak free.