Betta Thermal Compact heaters are constructed using high quality materials they have a reliable circuit to ensure heat output and maintenance of constant water temperature inside the aquarium. Temperature can be adjusted between 20 – 34 deg C. Advanced design. Manual temperature controller. Mains power indicator. Totally submersible. Waterproof double seal material for safety. Aquarium heater / thermostat 25w – for aquariums from 5-20litres.