Once I make my 10 gallon into a bare bottom tank and start breeding cories, I am going to put my 50 watt submersible heater in there. My question is, how much wattage for a heater should I get for the 20 gallon?
100w will be perfect - if it does get cold it will heat it back up right away. But, you could also go with a 150 if you wanted a little bigger a little better. A 100 will work as good for a little cheaper.