The Aqueon Submersible Glass Aquarium Heater is a submersible, shatter resistant glass heater designed for both freshwater and saltwater environments. With heat settings between 68 – 88 degrees Fahrenheit, aquarists have the freedom to adjust their tank based on the health and inhabitants of the tank. Accurate to within 1 degree Fahrenheit. The Aqueon Submersible Glass Aquarium Heater comes with a small LED light that illuminates when the heater is activated and a automatic shut off function to ensure the tank never gets overheated. The heater can be positioned with suction cups either vertically or horizontally and the 50 watt model is suitable for tanks up to 20 gallons.