Since you're talking about a discus tank, you can get by without huge over filtration simply thru water changes. While filtration is still necessary, clean, nitrate free water from water changes is still the best. If it were me, I would get a a canister filter with a moderate turnover, tee off the return line to make an outflow for a drip emitter to drain out water. Then I would get a automatic top off controller, you know, the ones made for replacing evaporated water from saltwater tanks. Hook this baby up to a pump, place the pump in your water change reservoir, place the float switch in the tank, and you're done. Automatic water change. I have well water without chemicals in it, so instead of hooking my controller to a pump, I have it hooked to a solenoid valve that is tied straight to a water line. My tank also has a sump, so the float switch is in it. As the sump level lowers, it is automatically refilled. Mine does 2 gph 24/7 on the 125 gal. tank with 13 discus in it. The fish do great with it, as the water parameters stay very steady. 
