the Thermal switch is a PT6 Master Flow auto-adjustable thermostat i bought at Home Depot in the roofing section (A reverse thermostat). I installed it under my hood away from direct airflow and wired it up to my fans and set it up to come on when the air space under the hood is just under 78 F it works really well the fans are only on when they are needed. This cut my evaporation in half and cut down on power consumption.
My tank temp stays constant only varying from 78.2 F to 79.4 F