Yes, poor water quality will have a negative impact on your fish. However, the problem for an AC300 pulling water has no effect from the depth of the tank. Only the height of the water line. If I were you, I'd add one or both of the AC70s back on the tank, and keep them there. The FX5 will add to it, but is a little much for a tank that small.FisHaRNekEd;1306630;1306630 said:But does not poor water quality cause the likleyhood of more pathogens to take over ?