Cobalt Accu-Therm Cobalt Accu-Therm 250 Watt Heater The all new Cobalt Aquatics ACCU-Therm fully submersible heaters feature an easy to set thermostat with and ON/OFF indicator light that is Triac equipped that turns the heater on and of at lower voltage, and magnetic contacts that ensure positive contact and release of the thermostat switch every time. All of these features are have been engineered to extend life and reliability of the thermostat and ultimately the heater. The tube is made of Borosilicate glass for superior heat and shock resistance and surrounds a high quality ceramic heat radiator that provides even and the best heat distribution from the heating elements. Perfect for freshwater and saltwater aquariums. Accurate to +/- 2F.