20$ here to fill a 20lb tank....eeeeeeewwwww...........that works out to $3.50 and hour for heating. Propane not cheap, about $14 here to fill 20lb tank. Guess I will rule a propane heater out, have no gas service here, so that makes solar or an electric heater.\
Saying that however, how long doe sit take to heat the pool from low 70's up into the 80's?
This is why i converted the heater to natural gas, 1$ per hour vs 4$ for propane per hour..
For my pool size i can raise the temp ~2-3 deg an hour (with the solar cover on)