In my 20g QT I use a penguin sponge filter/powerhead (petsmart), a 50w heater, air pump and air stone, and two small pieces of pvc (home depot). That's it, no rock or sand. I have a HOB power filter with carbon just in case but haven't used it yet. I also painted the outside bottom of the tank to make cleaning debris easier. The QT tank is in the darkest and most quiet room of the house.