Emperor Aquatics BioPRO Filters provide exceptional bio-filtration and are designed for pond applications with heavy fish loads. Each BioPRO Pond Filter features BioCELL bio-media, made of neutrally buoyant, "high-impact" polystyrene. During filter mode the BioCELL media bed is stationary inside the filter, when backwashing the media bed is gently lifted allowing for a better solid waste removal. BioCELL's design combines the right amount of self-cleaning with a highly protected surface area (198 ft²/ft³) for nitrifying beneficial bacteria colonies. BioPRO Filters provide complete mechanical and biological filtration for ponds up to 16,800 gallons with heavy fish loads. BioPRO Filters are biological filters and must be positioned after a mechanical filter. The BioPRO Pond Filter must be positioned after a mechanical filter to prevent debris and heavy solid waste from entering, collecting and fouling within the filter. Install a skimmer box before the BioPRO Pond Filter or install a Tadpole Filter before the water pump for the BioPRO to achieve optimal bio-filtration.