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Filtration System

Settlement chamber. A vortex barrel provides greater settlement; water from the bottom drain enters the vortex barrel at midpoint. The water moves in a circular movement allowing solids to gather in the center this allow the heavier particles to settle to the bottom, where they can be removed. Clean water exits this barrel at the top.

Mechanical filtration. Most filter media have a mechanical function. In addition to baffle plates which slow the incoming water, brushes or matting can be used to strain the water of solid waste before leaving this section of the system.

Biological filtration. This relies on specific bacteria to break down toxic waste products to less harmful substances. There are two stages in the breakdown of ammonia, each stage involving different types of bacteria. The first stage is the breakdown of ammonia to nitrite by nitrifying bacteria, most important of which is Nitrosomonas. The second stage is the conversion of nitrite to nitrate by Nitrobacter. Both of these groups of bacteria are aerobic (needing oxygen to live), sediment building up in the filter will deplete the oxygen levels so it is important to keep sediment to a minimum by having a settlement chamber first and by cleaning the filter out occasionally (but not using tap water as the chlorine will kill the bacteria). A variety of different media are available to put in the filter, materials such bio balls, matallas and spring flows are all suitable as they provide lots of surfaces for the bacteria to live on. A biological filter will take weeks or months to mature; cultures of nitrifying bacteria are widely available and will speed up the process.

After the basic filtration needs are satisfy, chemical, UV filtration and sand filter are added benefits to the pond.

Chemical filtration. Activated carbon removes chlorine, tastes, odors, colors, pesticides, heavy metals and other impurities. You should replace the carbon every three months. Zeolite absorbs ammonia from the water. If a large biological filter is present Zeolite should not be needed, but it is good to use while the biological filter is maturing or isn't big enough for the pond.

Sand filter. Some Koi keepers use a sand filter as a final stage to 'polish' the water. The water is passed under high pressure through sand and comes out very clear, bacterial activity also takes place in the sand filter. Sand filters are expensive though, and you can't make one yourself because of the high pressure involved.

UV filters. Controlling algae, biological filtration turns ammonia into nitrate which is harmless to fish (unless at extremely high levels) but the disadvantage of this is that algae love nitrate and you get an algae bloom. There are two types of algae problems, green water and blanket weed. Green water is caused by microscopic algae in the water, it is not harmful to Koi, actually it is beneficial, the Koi eat the algae and it enhances their color, but you can't see them! An ultra violet (UV) filter kills the algae. As the water passes through the light it disrupt the algae cells internally, killing them or preventing them reproducing.

Cleaning. Filters need to be cleaned occasionally to remove sediment, take this into account when building one. Add a bottom drain to each filter chamber so that sediment can be let out, it makes cleaning much easier. Another thing that makes cleaning easier is to put filter medium in net bags, not just pour it in all at once, as it can then be more easily removed, one bag at a time. Use pond water to clean a mature filter, tap water will kill all the bacteria and you will have to let it mature all over again.