Ficious
Fish Addict
a fan blowing on it constantly has to help for something
Take a few used soda/water bottles and clean them thoroughly.
Fill them with water and freeze them.
When the temp is too high float one or two of them in the tank. If the temp gets too cold, the heater will kick in.
You can also place a fan to blow over the water surface.
It might cause evaporation so be sure to top the tank off.