Adjustable heaters are part of the basic technical equipment of an aquarium. Heating rods, which are installed underwater in the interior of the aquarium tank are often used for temperature control. In aquaristics, these bar heaters often have a glass shell. Adjustable heaters made of unbreakable special plastic are much more robust and resistant to falls or other acts of violence than the ones made of glass. An adjustable heater automatically shuts off when the desired water temperature in the aquarium is reached, and it automatically turns on again when the water temperature falls below the value set on the aquarium heater.