beef with fluval 3

[littlelil]

I have submersible fluval 3 Plus and its supposed to suck water in through the bottom where there are grates and out the top, where the pump is. However, this is not what mine does. It, in fact, sucks the water through the top of the canister, where the holes are to press to unhook the pump from the canister. This makes sense since there is more power for water to flow through near the top because that's where the pump is. However, the problme is that 3/4 of my filter media is essentially untouched! 1/4 was completely clogged with gunk, while the other was clean as a whistle!!  Am i missing a part? Is this how everyone else's works? This is very surprising/disappointing since my fluval 205 canister filter is like, the greatest thing in the whole world..