Aqueon Pro Aquarium Heaters are built to deliver consistent heat. Each unit is made with a durable thermal plastic shatterproof housing and equipped with an electronic thermostat. The thermostat has an auto shut off safety feature, when the top of the heater tilts below the bottom of the heater, it will shut off. Additional features include adjustable heat settings and LED heating indicator that illuminates when actively heating. The suction cups make horizontal or vertical installation quick and easy. Pro Heaters are fully submersible and made for use in freshwater and saltwater aquariums. Available in five sizes to accommodate various aquarium sizes.