Aqueon Submersible Aquarium Heaters are designed for fresh and saltwater aquariums. Each unit is fully submersible, shatter resistant and equipped with an electronic thermostat that provides accurate and reliable heating. Additionally, there is an adjustable heat settings ranging from 68° - 88°, an LED which illuminates when actively heating and a built-in auto shut off function that prevents the heater from overheating. The suction cups make horizontal or vertical installation quick and easy. Available in five sizes to accommodate various aquarium sizes.