BioMaster² 250 Thermo External Filter by Oase (UK) LtdThe BioMaster 250 Thermo filter is great for keeping aquarium water clean. It has special filters that use Hel X and sponges to make sure the water stays healthy and clear. It also comes with a HeatUp 150 adjustable heater to keep the water at the right temperature. For Aquariums Up to 250 Litres: Perfect for medium sized fish tanks. Easy to Clean: The EasyClean pre filter makes cleaning simple and quick. No Leaks: Automatic shut off and safety valve