^ +1. My biggest heater is a 1000W, which runs on it's own controller, and I have my ACIII as a failsafe. I unplug the 1000W except in the winter, and instead have a few 150W. Even if the 150W heaters completely locks up, it isn't enough by itelf to cook my tank. However, pre-controller, I lost a whole QT full of fish to a locked on heater.