click here to get 34 % discount: www.amazon.com Sunterra 300207 Pond UV Bio-Filter 2000 Gallons, Black 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 ponds ecosystem. This filtration system must match both the power of the pump and the volume of the water garden. All Sunterra filters use mechanical and biological filtration. The mechanical filtration process uses foam filters to trap debris. While the biological filtration uses biological ball (bio balls), that have large surface areas used to nurture beneficial bacteria. This beneficial bacteria converts harmful pathogens into useful nitrates. Both types of filtration work together to provide a clearer and healthier pond. The Sunterra Bio-filters utilize a dual filtration system consisting of both mechanical (foam filters) and biological (bio balls) processes. UV Pond filters are for ultimate filtration performance. They combine the same features of mechanical and biological processes of other Sunterra filters and have the added benefit of ultra-violet light filtration. UV radiation eliminates the algea that survive the normal flitration process, creating a clearer and healthier water garden.