Maintain the temperature of a freshwater or marine aquarium to help keep plants and fish healthy. 100-watt heater for tanks up to 25 gallons. High-quality insulated glass with easy-to-read analog design is simple to operate, just turn the knob to adjust the temperature. Attach to the side of the tank with suction cups. Double-insulated and fully submersible, this heater is designed for years of use.