I agree with an above poster. AC's are much easier to access to clean. In my 125g I have a FX5 in the middle, AC110 in one corner, and fluval submersible FU4 in the other corner. THat way there's a current throughout the entire tank. The AC's really push the water around, and do a great job oxygenating (is that even a word??lol) too
The main bacteria load is in the fx5. The AC just helps out