The all new Cobalt Aquatics ACCU Therm fully submersible heaters feature an easy to set thermostat with andON/OFF indicator light that is Triac equipped that turns the heater on and of at lower voltage to extend life and reliability of the heater and is computer tested and accurate to ?2?F. 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. 3 year warranty.