A contained body of water is subject to conditions such as dirt, insects, algae, and decomposed vegetation that affect the water clarity and health. A filtration system is needed to balance the pond's ecosystem. This filtration system must match both the power of the pump and the volume of the water garden. Our bio-filtration products utilize a dual filtration system consisting of both mechanical (foam filters) and biological (bioballs) processes. The bio-filters watertight pressure containers ensure leak proof performance, while our unique self-cleaning feature ensures filter performance is always working properly. No. 337106: Prefilter box No. 300106: 1000 GPH pressure filter No. 320106: Replacement filter for prefilter (model No. 337106) No. 330106: Replacement filter for pressure filter (model No. 300106)