Hydor Theo 300 Watt Aquarium Heater is a fully submersible, shatter-proof glass aquarium heater.Maximum security: THEO is shock resistant thanks to the PTC heating element and the shatterproof glass tubeFree positioning in aquarium with supplied suction cupsSelf-limiting: the patented PTC heating system guarantees operation in complete safety because in case of dry running there is no danger for damageTemperature range: 70-94 degrees Fahrenheit