Well, most people in this forum recommend frequent water changes with that size tank. I would too if you have the time, however I do have a 2.5 mini bow that I have a pennplax smallworld filter in with a Marineland 25 watt Visi-Therm Deluxe fully submersible heater in. So far they have worked for me. I have one male betta in the tank with one live amazon sword plant and an ornament The betta is happy and healthy so far.