Sharz, you have a rather common misconception that by overfiltering a tank it is OK to overstock it. That is simply not true. By overfiltering a tank you can promote lots of water circulation and will pick up more of the fish solid wastes in the filter but it does nothing for water quality. Water quality is really achieved by doing enough water changes often enough to take care of the waste that builds up in the tank in the form of nitrates. If you overstock a tank, you can get away with it if you are willing to do frequent huge water changes. We are not talking about 30% weekly changes here but truly large water changes many times each week for extreme overstocking. Filters do nothing to remove the chemicals that come from fish being present in a tank, only water changes can do that.