All About Filters

All About Backyard Pond Filtration

Filtration is used in backyard ponds to achieve clear water and healthy water for fish. There are three basic ways of filtering pond water. Mechanical Filtration, biological filtration, and U.V. Most filters designed for backyard ponds will filter water both mechanically and biologically, some will filter water using all three methods.

Mechanical filtration is collecting suspended particles/ debris/ algae etc. on some type of media such as foam, brushes, beads, etc. by pushing/ pulling water through it where it can be removed by backwashing, manually cleaning or draining. Examples of mechanical filtration include skimmer nets or baskets, filter pads in skimmers, pre-filters on pump intakes and the first "chamber" or point of water entry in a biological filter. The result of proper mechanical filtration is improvement of water clarity. Proper mechanical filtration also results in better biological filtration by keeping biological filtration media clean. This means if the pond water is unclear due to particulate matter, mechanical filter media should be cleaned as frequently as possible. This keeps the media clean allowing it collect debris more effectively where it can be removed from the pond. Frequent cleaning is important to the pumps longevity if the filter is on the intake. Once the pond water is clear maintenance becomes far less frequent as the only thing accumulating on the media is algae and bacterial growth. Cleaning is only needed when the flow of water is impeded.
Biological filtration is encouraging the growth of aerobic (oxygen dependent) bacteria colonies. These bacteria assist in breaking down organic waste that occurs naturally in an outdoor pond. This naturally occurring organic waste is made up of fish waste, old growth from pond plants, and material that gets blown, or washed into the pond. All ponds will grow this beneficial bacteria without any human assistance. They grow/ colonize on nearly any surface in the pond, waterfall, filter, etc as long as there is water with oxygen levels high enough to support them. Since they thrive on oxygen they grow best near moving water. A great example are the rocks in the waterfall. Many pond owners may not realize how beneficial the film on these rocks is and constantly scrub it off. This is disrupting a good source of biological filtration! Pond owners should understand the "Nitrogen Cycle" to fully understand biological filtration.
Nearly any and every filter is a biological filter. Water pushed or pulled through media or inner surfaces of the filter will be oxygen rich and encourage bacterial growth. The key to biological filtration is to leave any media and/or surfaces in the filter "untouched" as long as it remain "unclogged" with water passing freely through it. It takes several weeks for bacteria colonies to fully develop on new media or to return from winter dormancy, so the longer the media remains undisturbed the better. Conversely though if/ when debris begins to "clog" the media blocking the free movement of water, the environment becomes less oxygen rich and beneficial bacteria growth is discouraged. The results of good biological filtration is high water quality not necessarily clear water. It keeps naturally occurring toxins such as ammonia and nitrite at low enough levels for fish to thrive, though it may actually increase"nitrate" levels and encourage algae growth or green water. New pond owners may wonder if their biological filter is working properly. Healthy fish are the best indication of good biological filtration Veteran pond owners know this difference between water clarity and water quality. Typically a good "bio" filter will provide both.
The best "bio" filters have some type of mechanical filtering element to keep the water passing through the biological filter media as clean as possible. This minimizes the frequency of washing or backwashing the media. Examples of biological filtration are "gravity- return" filters which are containers that utilize a variety of materials for media. Many biological filters operate "pressurized" typically utilizing small beads, balls, or plastic pieces as media. Cleaning/ backwashing should be performed minimally just to keep media clear and free flowing. Always use a bacterial product to help relatively quickly "recharge" the filter with fresh bacteria seed after any maintenance to the filter.
U.V. (or ultraviolet light) filtration is utilizing a high intensity ultraviolet light to destroy unwanted cells or organisms in pond water. Water is pushed/ pulled through housing or a chamber. The U. V. lamp is in the chamber protected from water by a sealed glass tube. The glass is a high quality quartz which allows a maximum amount of light to pass through it. As the water passes by the lamp suspended algae cells are irradiated rendering them incapable of reproduction, eventually eliminating them entirely. This ensures very clear water. Proper flow rates are critical for proper functioning. Water passed by the lamp at slower flow rates will additionally kill larger organisms such as parasites and bacteria that may attack fish. They have no effect on beneficial bacteria colonies since they are attached to surfaces and do not pass through the filter in free flowing water.See "All About U.V. Filtration in Backyard Ponds".
A universal requirement of all filters is a pump of some type to push/ pull the water through the filter. Some small filters come as a complete unit with pump and filter in the same housing, or possibly packaged together as a matching unit. A majority of filters are sold without a pump and require one to operate.

For how to choose a specific filter click here.