A 50 watt CHE would be plenty for a 20 gallon. Just set it on a thermostat. I converted a 75 gallon for my yearling. For the lid I cut wood to fit and glued foam board to the bottom to protect the wood and help insulate it. This may be an option for you too.Ok my first question is, what watt heat bulb or Che should I go with mounted through the lid in the tank itself?
and then can I use plexi glass on the lid to keep it insulated or night it melt or reflect light in a bad way?