May need to get a chiller. Every piece of equipment in the tank is giving off heat as it uses electricity. A 50w pump is basically the same as a 50w heater. So all your equipment in and around your tank is going to heat it up above local temp. May only be a couple degrees but if you really want to keep your tank stable, get a chiller and keep your heater and get a controller that has heating and cooling plugs. You never know when something weird happens, window left open in the winter, whatever. The stability will be worth having both, you'll be able to sleep knowing that your temp is going to stay where it needs to be.
Hope I answered your questions!