Whether you are keeping a small pond with a few fish or a large pond with a koi variety you will need to make sure that you adequately filter your pond either through a koi pond filter box system or a pressurized pond filter. A garden pond filters job is not to only keep your water clean and clear but to act as a sewage system for your pond and at the same time becoming a home to the millions of bacteria that are helpful to your pond. If you are purchasing a pond uv sterilizer then these bio pond filters are essential as the uv sterilizer does not actually break down algae but clumps it together ready for the bio pond filter to break the algae down. Our pressurized uv pond filters already come with a uv clarifier built into the pond filter system allowing for the process of coagulating and breaking down the algae with less pond equipment.