MINI Temperature Controller Thermostat 25W Heater Heating Aquarium Submersible for 5~20L 25W AC100~120V, for 5L~20L fish tank For aquarium in-door use only. Check power supply, power outlet, and voltage in comply with rated values. To set desired temperature, turn the adjustment knob of Thermostat to the desired temperature. Put Heater into aquarium, submerged in full, at a position with good water circulation.