The koi pond filter system can be divide to 3 Parts:

Water inlet: Bottom Drain and Skimmer

Filter: Mechanical and Bio

Water outlet: Waterfall and Jets (TPR)



1. Bottom Drains :

Bottom drains (BD) are openings in the bottom of the pond where sinking waste is pulled out of the water and into the mechanical filtration on the

outside of the pond.

PROS:  BD’s are a must to remove sinking debris.  They require no maintenance. 

CONS:  If not installed correctly, they will leak.  If the air dome is not set at the proper height, small fish can go down the BD and into the mechanical filtration and die.


2. Skimmers

A skimmer is designed to suck floating debris and DOC off the top of the pond.

PROS: Skimmers remove floating debris before it has time to settle to the bottom of the pond. 

CONS:  Skimmers will suck in food before the fish can eat it.  Fish can injure themselves trying to get to the food.  If you do not have the type of skimmer that has a basket inside to catch the debris, small fish can go into the skimmer and get sucked into the mechanical filtration and die. Skimmer need to be installed in the correct location for each pond to work properly. 


  • B. FILTER:

Koi pond Filter is contain 2 different filters. Mechanical filter is to separate waste out of the water, and Bio filter is to convert Ammonia to Nitrite and to Nitrate.


There are many type of Mechanical Filter. Depend on the design and budget, we can use one in the following list (ranging from cheapest DIY to the most expensive but best in class RDF)


1. Sand and gravel filter:

Usually a 55 gallon barrel with 5 gallons each of large gravel, medium gravel and pea gravel, water travels from the bottom to the top and out to the pond. A 1hp. Spa blower is used to clean the gravel.

PROS: This is a cheap and effective way to filter out particles and is easily DIY. 

CONS:  It is ugly and not easily hidden.  It does not filter very small fines.


2. Pressurized Filter:

Bead filters are used as mechanical and biological filters. They do not have enough surface for the bio to live in it, and when back wash  with the blower, Bio will be push out along with poop. It can be used just as Mechanical filter alone or couple with Sieve in front of it.

PROS: They are easy and fast to clean. 

CONS:  They are expensive and do not work very well for biological filtration unless the media is kept very clean, meaning they need to be backwashed often.


3. Sieve:

There are several types of sieves on the market.  Water enters into the sieve and flows through a wedge wire screen, separating the trash from the water. The trash is removed from the water flow, so it does not add nutrients back to water.  The majority of the trash is automatically removed so there is little maintenance.

PROS:  Sieves do a great job of filtering out waste and reduce pond maintenance time drastically. 

CONS:  Sieves are expensive and required to clean weekly.


4. Rotary Drum Filter

A Rotary Drum Filter (RDF) is the best mechanical filtration in terms of the being able to remove the smallest particles in the water.  An RDF is basically a box with a drum on the inside.  As the water enters the drum from the pond, the screen on the drum clogs up causing the water level in the box to lower which turns on a spray bar to clean the screen.  The waste that is washed off screen is automatically sent to waste.  The owner must remove large leaves occasionally but not much other maintenance is required.

PROS:  RDF’s reduce pond maintenance to almost no manual time on the part of the owner. RDF’s filter down to the smallest micron available in filters so the water is much cleaner. 

CONS:  RDF’s are very expensive, and need to setup correctly to avoid malfunction. 




1. Moving bed:

A moving bed is floating plastic media such as K1, K2, MB3 contained in a 55 gallon barrel with air in the bottom that boils the media.  Bio bugs attach to the media to clean the water.

PROS:  Easy to DIY, cheap to build, efficient.

CONS:  Hard to hide, ugly, and sometimes it’s hard to contain the media.


2. Bio Chamber:

A chamber box contain Bio materials to provide a place for the bio to live in and converting Ammonia to Nitrate.  Japanese Mats, brushes, and Ceramic bio (such as ceramic Lotus media) can be used as biological filtration as long as they have very clean water. The Bio chamber need to be installed after mechanical filter.

PROS:  They are cheap and easy to DIY. 

CONS:  Size of the chamber is depended on the type of media. J mats and Brushes are cheap option, but need a very big size chamber to make it work (1/3 to 1/2 size of the pond). Submerged ceramic media works more efficient with much smaller footprint, but  the cost is expensive.


3. Shower:

One of the most efficient biologicals filters used.  It is a stack of boxes that contain feather rock, lava rock or some type of ceramic rock media.  The water flows down through the boxes and back to the pond.

PROS:  Showers can be easily DIY and cheap or you can get them as expensive and pretty as you’d like.  Very low maintenance.  

CONS:  Showers are big and bulky and usually not pretty.  They can be very expensive.




1. Waterfall:

If Bio shower is not be used as the way to return water back to the pond, or waterfall is a part of the design, The waterfall can be construct with a use of Waterfall outlet and rocks to create the design of natural waterfall. Helix moving bed waterfall is one of the best waterfall in the market.


1. TPR (Tangential Pond Return):

TPRs are often be used as water return to create current on the pond. Koi are river fish and they love to swim against the current. Having a great current flow in the pond design will help to push the waste to the bottom drains (Clean bottom) while improving koi body when pushing them to swim all day long.



Having a proper design pond with a great filtration ( Mechanical and Bio) are the key for a successful koi keeping experience. There are many ways and combinations to create a healthy pond system for your budget and your need. At the end of the day, the most important of koi keeping is maintaining your water quality.

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