Tetra Submersible HeaterTetra HT Series Submersible Heaters are created especially for ease of use in your aquarium. An electronic thermostat automatically adjusts the heat output to keep the water at a constant 78 degrees F, so all you have to do is plug it in! Easy to control with no adjustment required Fully submersible and shock resistant Maintains constant healthy water temperature 2 year manufacturer warranty An electronic thermostat automatically maintains water