Filtration is essential for ponds to establish and maintain healthy water and fish. Deciding what type of filtration your pond needs depends on the level of water quality you wish to achieve. Before you can find a solution for your unique pond setup, it is important to know what purpose each of the filters serve.

Types of Filtration

• Mechanical filtration is the simplest form of filtration. It works by physically trapping solid debris from the pond by straining water through through media of varying densities and coarseness.
• Chemical filtration consists of media such as activated carbon-charcoal and zeolite to absorb and remove odors, organic toxins, and excess nutrients from your pond water. Chemical filtration works best when used in combination with both mechanical and biological filtration.
• Biological filtration, or more accurately: biological conversion, is not only essential for ponds, it is the most effective method for removing toxins from ponds. Biological conversion relies on naturally occurring beneficial bacteria and biological media to convert deadly fish and other organic waste into compounds that are utilized by pond plants. Biological conversion also helps to eliminate the waste products which lead to excessive algae growth.

Styles of Pond Filters

• Submersed Filters are generally larger and more versatile than intake filters. A reasonable unit may use a variety of filter media including coarse and fine pads for mechanical filtration, carbon or zeolite for chemical filtration, and maybe even special media for biological filtration.
• Pressure Filters are resealable canisters that may be filled with a variety of media for mechanical, chemical and/or biological filtration. They are most commonly used on the output side of the pump. Many in-line filters may also be operated either submerged or above ground.
• External Filters are generally the largest of pond filters, and are located above ground, or partially buried, near the pond itself. Water from the pump’s output enters the filter, flows through the filter media, then exits. External filters may be operated with a variety of media, and generally use biological media. External filters are often considered the most efficient form of biological filtration, and above ground installation makes unit easy to clean.
• Skimmer Filters are mechanical filter devices, connected to the intake line of a pump, that continuously draw and collects floating debris from the surface of the pond, which allows the water to then be directed to the pond's filtration system.

Different styles of filters are typically used in combination to take advantage of each filter’s strong points. An effective filtration setup is to attach a submersible filter, filled with coarse media to pre-filter debris and protect the pump, on the pump’s intake; an in-line filter (like a pressure filter) on the output of the pump; an ultraviolet clarifier, to kill free-floating algae and microscopic parasites, on the output of the in-line filter; and finally an external filter, filled with finer media to catch smaller particles and biological media to improve water quality by reducing ammonia and nitrites, on the output of the ultraviolet clarifier. Such a complete system provides the best filtration, and also results in longer times between cleanings.

The bigger a filter is, the more waste it can process between cleanings, and the better fish can be safely maintained. As a rule, you can never have “too much filtration.”