The Fluval M Type Submersible Heater delivers precise, reliable heating for freshwater and saltwater aquariums. Featuring shock-resistant borosilicate glass, a computer-calibrated thermostat, and an exclusive mirror finish that blends into your tank, the Fluval M Series keeps water temperature stable while staying nearly invisible in your aquascape. Available in 50W to 300W options for tanks up to 80 gallons.