The Fluval 25 watt compact aquarium heater is an automatic submersible heater for use in indoor aquariums. Without any adjustments needed it is designed to reach but not exceed the pre-set temperature of 26C (78F) subject to ambient room temperature. The exterior is made of a tough polymer so that it will not crack or break like traditional glass sleeve heaters. The heater is ideal for aquariums up to 6.6 gallons (25 L) and can be used in fresh and saltwater tanks. The heater will increase aquarium temperature by up to 4 degrees celcius above ambient room temperature.