Koi Ponds and Filters

Koi Ponds:
Introduction to Filtration:
Koi Pond Filtration:
Advanced Topics:

Koi Ponds:

What is a Koi Pond?

A Koi pond is an enclosed, recirculating, freshwater system for keeping Koi (Japanese fancy carp).

This subject area has been the hardest to describe. I am not trying to offend anyone. But, before we go any further, it is important to note that when KOI.NET refers to a pond it is considering a "pond for Koi." Please do not confuse a Koi pond referred to here with a "natural garden pond," a waterlily pond, or a small water accent in the garden. There is nothing wrong with any of the these. It just that here, the purpose of a pond is to provide a healthy home for Koi. Koi can live in the others, but not in the numbers that necessitate a Koi pond.

A Koi pond should serve two main functions;

Neither of the above is dependent on the other. You can have healthy and happy Koi in a "pea-soup" green pond, or you can have diseased and dying Koi in green water. Having "crystal-clear" water is not an indication of a healthy pond. Water is an excellent solvent. It is possible to have unhealthy, toxic, crystal-clear water. In fact, you might have pond water so unhealthy that even algae would not grow in it!

In addition, most Koi ponds are an attractive addition to the garden!

The way we achieve the above two functions is mainly through "biological filtration" as opposed to using "mechanical" filtration and/or "chemicals."

Swimming Pool Filters.

One of the reasons swimming pool filter systems do not work very well on Koi ponds is that they are designed for mechanical and chemical filtration of water. Swimming pool filter systems rely on a pump that is operated for a set time each day. Pumps used for biological filters are required to run 24 hours a day. Most people who purchase swimming pool pumps for Koi ponds are "shocked" at the increase in their monthly electrical bills.

Small Commercially Available Pond filters.

Let me warn you about some commercial pond filters available through nurseries, water garden supply, and internet catalog sales. The manufacturer, like most companies, are in business because there is a demand for these product . Some product descriptions, as advertised, may seem like the solution. But seriously, who would you rather trust? The claim of a manufacturer or somebody who lives near you with a successful fish pond. KOI.NET feels that your "best" source for information on proper filtration is from a person, in your area, who has successfully kept fish healthy in their own pond for several years. The best place to locate people like that is through a Koi club in your area.

Commercially Available Koi Pond Bead filters.

Since the introduction of the BubbleBead filter back in 1996, other commercially made bead filters for Koi ponds have become very popular. Originally, some of these new bead filters were nothing more than swimming pool sand filters with plastic beads for media. Over the years there has been some design advancements by a couple of companies. Most notably is the replacement of plastic beads with small plastic tubular media with increased biological surface area that is less prone to clumping problems. Talking to many owners of these filters, like the original BubbleBead filter, an ultra-violet (U.V.) sterilizer is needed to control green water.
There are other types of commercial Koi pond filters that are not enclosed media pressure filters like bead filters. Most notable is the Nexus Eazy moving bed filter with its Kaldnes K1 media (advance filtration design and very expensive) and the Bakki Shower filter with Bacteria House ceramic media (also very expensive).

Koi Clubs.

The advantage of Koi clubs is that most clubs provide you with the opportunity to visit several private Koi ponds. By visiting and asking questions, you should be exposed to several ways to achieve biological filtration. There is not just "one way" to achieve a healthy pond. Hopefully by visiting several ponds you can "borrow" ideas and avoid the mistakes made by others.

Design Considerations for a Koi Pond.

The rest of this page focuses mainly on filtration related topics. Below are pictures of a variety of ponds that represent the above design considerations. Please check back, because this area will always be "under construction" with new pictures added as they become available.

Introduction to Filtration:

Most ponds have been built as part of the general landscaping. Later on, some goldfish were added to give the pond some life. Then those beautiful Koi were discovered. But now suddenly, when there is brightly colored fish to look at, green water is a major problem.
What is needed is a biological filter. This will take the wastes from the fish and process them naturally to produce clean water. This is done through microorganisms that develop in the biological filter. Mechanical filtration is also important. The less solids that go into the biological filter, the better it is for the microorganisms to concentrate on the dissolved wastes like ammonia.
As stated above, a swimming pool filter will not work on a fish pond. The reason is, in a swimming pool you use chlorine, and the pool water has very little solids and ammonia (fish wastes) in it. A swimming pool filter used on a fish pond will require frequent back-flushing. Also a high powered pump will be required to push the water through the filter. Remember, you will need to run the pump 24 hours a day, and this will show up on your electric bill.

Koi Pond Filtration:

Koi pond biological filters can be built as either an "up-flow" or a "down-flow." The "out-of-pond" designs are a little easier to maintain and can be added to an existing pond. A good reference on filtration is The Tetra Encyclopedia of Koi.


The Sequence 1000 produces a maximum flow rate with minimal electrical consumption when compared to swimming pool and cheaper submersible pumps.

For more information and a distributor near you, call:

Multi-Duti Manufacturing, Inc.
e-mail: Sales@mdminc.com

Be sure to mention you saw it on KOI.NET!

Another good, efficient, "swimming pool" style of pump is the
Sta-Rite LT 1/6 HP, 3.7 amps, 2400 gph.

For a distributor near you:

Sta-Rite Pool/Spa Group
1-800-752-0183 (North America)
414-728-5551 (International)

StaRite Pump

Rio Pump Rio Pumps are high-flow, very efficient, submersible (no oil) magnetic drive pumps. Very affordable for small ponds. Higher Performance RIO pumps.

For a distributor near you, call:

Westcoast Aquatics
1-805-499-7866 Be sure to mention KOI.NET!

A new energy efficient swimming pool style of pump is the Wave Series. Electrical consumption starts at a low 2.1 Amps.

For more information and a distributor near you, call:

W. Lim Corporation
e-mail: WLimCorp@WLimProducts.com

Wave I Pump

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Advanced Topics:


Web'ster: (Richard Renshaw), rrenshaw at playkoi dot com
Copyright © 1996-2013, Richard L. Renshaw, Revised January 30, 2013

An in-pond, down-flow biological filter:

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Out-of-pond, up-flow filter:

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An out-of-pond, down-flow biological filter:

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More out-of-pond biological filters:

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