Aqueon, Submersible Aquarium Heater, 300 WattProduct Description Aqueon submersible aquarium heaters are made from thermal shatter resistant quartz glass and designed to absorb impacts, making them extremely durable. An electronic thermostat stops heating once set temperature is reached. A power indicator light turns on when the unit is heating and is equipped with a 6 foot power cord. UL approved, the heater is also programmed to turn itself off when not properly submersed to avoid overheating