The new, easy-to-use Tetra HT30 submersible heaters created especially for aquariums up to 55 gallons. The electronic thermostat automatically adjusts heat output to keep the water at a constant 78F. All you have to do is put it in the aquarium and plug it in! Indicator light lets you know when water is being heated. Printed heater tube blends in with aquarium background. Strong borosilicate glass tube is heat and shock resistant. Info from Tetra