The Theo fish tank heater has all the essential features for the precise and safe maintenance of the water temperature in your aquarium. The exclusive technology and the high quality of components guarantee a long life. The aquarium heater is submersible, anti-thermal shock, highly resistant and features a graduated scale for precise temperature regulation. It can be positioned horizontally or vertically. The Theo aquarium heater also features self-control limiting technology. So, if the fish tank heater senses abnormal functioning the patented PTC heating system guarantees completely safe operation in case of dry running.