The experts at That Fish Place have put together this guide to help you wade through the waters of pond filtration. Below you will find information on Submersible Pond Filters, External Gravity Pond Filters, External Pressurized Pond Filters and Surface Skimmer/Waterfall Pond Filtration Systems.Submersible Filters
Submersible Pond Filters are commonly used on small ponds and water features and are noted for their ease of installation. These filters are a favorite of people with patio ponds or barrel ponds. As the name suggests, these types of filters sit on the bottom of the pond and filter the water internally. Water is drawn through submersible pond filters by a submersible pump, which can be attached to the filter either internally or externally, and then discharged into the pond. Pond filtration generally takes place through a replaceable mechanical filter pad and a permanent biological filter. These filters must be removed from the pond for maintenance and cleaning, which is why they are not recommended for heavily stocked ponds or ponds with high debris loads. The water discharge from submersible pond filters can simply re-circulate water into the pond, or power a fountain or small waterfall. Many submersible pond filters include a fountain kit with purchase. Some filter models also include an integrated ultraviolet (UV) sterilizer feature, which further aids in purifying and removing algae from your pond's water. These pond filters can be used in both flexible liner ponds and pre-form type ponds. External Gravity Filters
In external gravity pond filters water is pumped from the pond or water feature into the filter, and then flows back into the pond by gravity. These filters must sit above the water level of the pond and are usually placed at the pond's edge. External gravity pond filters typically have a reusable/replaceable filter pad for mechanical filtration and permanent biological filter media. These pond filters are easily maintained and installed, and due to increased capacity for filter media, are generally more efficient and can handle larger debris loads than submersible pond filters. Some external gravity pond filters also incorporate ultraviolet (UV) sterilizers for further pond water clarification and algae removal. Unlike many submersible pond filters, external gravity pond filters require the purchase of a separate pond pump for operation.External Pressurized Filters
External pressurized pond filters allow the greatest flexibility in locating your pond filter. Unlike other pond filters, these filters can be placed further away from your pond or can even be partially buried to hide them into your landscape. The function of external pressurized pond filters function is wide ranging: from small to very large ponds. Basic pressurized pond filters consist of a sealed canister that is fed pond water through tubing from a pump. The water is then forced through a mechanical and biological filter media, then exits the filter and is returned to the pond. Basic pressurized pond filters need to be disassembled for cleaning and maintenance as flow decreases due to clogging. More complex styles of pressurized pond filters have backwashing ability. "Backwashing" is the ability to reverse the internal flow of the water and divert the outflow of the filter to a separate waste line away from the pond. By backwashing the pond filter, you can significantly reduce or eliminate the need to disassemble the filter for manual cleaning. Some external pressurized pond filters also incorporate the use of ultraviolet (UV) sterilizers into their design to further clarify and eliminate algae from your pond's water. External pressurized pond filters can be used on both flexible liner and hard pre-form type ponds. A separate pond pump is required for operation.Surface Skimmers and Waterfalls
Surface skimmers and waterfall pond filters are two part systems designed for use on medium to large flexible-liner ponds. The first part of this pond filtration system is the skimmer box. The skimmer box is constructed from rigid plastic or fiberglass and is attached to the pond edge at ground level outside the pond. A "doorway" is cut in the pond liner and the liner is sealed to a matching opening in the side of the skimmer box, which typically houses a net or basket to catch floating debris and a filter pad for mechanical filtration. Surface skimming traps leaves and other surface debris before it can sink into the pond, keeping the pond much cleaner. A submersible pump inside the Skimmer box sends water to the second component of these pond filters: the waterfall filter. The waterfall pond filter is typically located on the opposite side of the pond from the skimmer box. Water is pumped from the skimmer box to the waterfall filter where it passes through biological filter media and then returns to the pond, cascading as a waterfall. Another benefit is that all the components of this system, including the pump, are outside of the pond, allowing easy access to everything. All of the components are easily concealed with landscaping and rock work, creating a very natural looking installation. The surface skimmer and waterfall pond filtration method is the preferred method for larger ponds and is used by many professional pond installers.