It's a false assumption that one piece of flexwatt can properly heat an entire 20gal tank. That would be true only if the ambient temps in the room were in the high-upper 70's to low 80's to begin with.


What I would do would be to use the flexwatt to create the warm "basking" spot...and then use the ceramic heat emitter on the "cool" side to create an overall ambient warmth in the low 80's. A separate t-stat for each would be ideal, but at the very least a pair of dimmer switches for each heating unit and a close watch of temperature levels.