Cobalt Aquatics Mini-Therm compact and fully submersible heaters feature a constant ON design, specifically for small aquariums. The heater casing is made from a thermal-plastic polymer that is shatterproof. An internal ceramic heat radiator that provides even and the best heat distribution from the heating elements. Perfect for freshwater and saltwater aquariums and terrariums. Will raise recommended size aquarium temps up to 10° above ambient temperature.