I would suggest putting the diffuser at the 12 ft. level if you were only going to run it during the cooler temps. at night, a thermostat could be connected to the pump so it only operates at cooler temps.
http://www.amazon.com/Lux-Heating-Coolin...8428&sr=8-1

Last edited by adirondack pond; 03/01/12 11:14 AM.