Aqueon Submersible Aquarium Heater, 300 Watts, Up to 100 Gallons;

Aqueon Submersible Aquarium Heaters are made from thermal shatter-resistant quartz glass and designed to absorb impacts, making them extremely durable. A power indicator light turns on when the unit is heating and is equipped with a 6-foot power cord.  UL approved, the heater is also programmed to turn itself off when not properly submersed to avoid overheating and damage. This heater can be positioned at a vertical or horizontal angle and used in freshwater and saltwater aquariums. This 100W is for aquariums up to 40 gallons. Other wattage heaters are also available, 50W, 150W, 200W and 300W.