Next year I am planning on setting up a fish tank in my apartment. I was given a 20 gallon tank to use. My question is what type of fish is easy to take care of, fairly clean, and can live comfortably in a tank of that size. It would be nice to have a fish that might not need heat. Gold fish are simple and cheap but I have had them before and they are pretty messy fish. Also, what type of filter would you guys most recommend?