Best Koi Pond Filters in 2021: Reviews with Comparisons

Best Koi Pond Filters in 2021: Reviews with Comparisons

A pond filter is an indispensable part of any garden pond, even more so if the pond is home to your koi collection. A reliable filter system ensures that your water remains clean and clear. It also safeguards your fish from hazardous toxins. Pond filters remove debris from the pond and encourage the cultivation of beneficial bacteria. These bacteria help to keep the water clear of toxins.

Your pond water may look sparkling clean, but unless the filter has cleared the biological waste, your koi may suffer distress.

Fortunately, there are some good filters in the market that will ensure that your pond is clean and fish in good health. Let’s look at 5 of the best koi pond filters.

Best Koi Pond Filters: Reviews

OASE BioSmart 10000 Pond Filter

Designed for medium to large-sized koi ponds, the compact BioSmart 10000 has a 10,000-gallon capacity. It will comfortably support a well-stocked koi pond of 2,500 gallons. The filter foams have a large surface area. This ensures excellent filtration and promotes the growth of beneficial bacteria. The water flow is unimpeded, so there is plenty of oxygen flowing through the filter.

This filter has a multi-stage mechanical and biological filtration system. The mechanical filtration system has multiple media layers filtering out particles of various sizes. Biological filtration converts harmful ammonia and nitrites into less harmful nitrates. These serve as a food source for aquatic plants.

Convenient additional features include temperature and pollution indicators. The pollution indicator informs you when it’s time to service the filter. This is easily accomplished. All you do is switch off the pump, pull on the cleaning handles inside the filter lid several times. Then, allow the sludge to drain out through the waste outlet. The filter has a maximum flow rate of 2,700 gallons per hour.

The BioSmart also has a 24-watt UV clarifier to remove algae and harmful bacteria. It comes with a three-year warranty.

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AST Bubble Bead Filter

Similar in form and function to a sand filter, the AST Bubble Bead Filter is low maintenance and easy to keep clean. It has no internal moving parts, so you can expect reliable service from this filter for years. This pressurized filtration system comes in eight different sizes, so you can select the one that best suits your koi pond.

The system is prefabricated, so installation is simple. You just hook the system on, plug it in, and you’re good to go. It is also energy efficient in operation.

Bead filters offer superior mechanical debris removal due to the large size and the slow movement of water through the media. In addition, the AST bubble bead filter provides excellent biological filtration due to the large surface area on which beneficial bacteria grow.

Water enters the bottom of the filter via a three-way valve. It exits through the top of the filter.

Filter cleaning is easy; all you have to do is backwash. The system is automatic, and you simply set up times and sequencing for the backwash. In addition, you never have to replace the beads.

Bead filters will trap 100% of particles of 50 microns or more and 48% particles between 5 and 10 microns. Unfortunately, this unit lacks a UV filter, so you will have to buy a UV light as an add-on if you want one.

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TetraPond 26596 Waterfall Filter, Up to 1000-Gallon

Looking for a waterfall filter for a small pond? You can create a pretty water feature or a small water garden with the TetraPond waterfall filter. Enjoy the benefits of clean and well-aerated water at the same time. The pump is easy to hide behind rocks and plants to look like a natural water feature.

The water rises up the base of the pump through a fibrous mat that collects debris. From here, it goes through the lava rock, or if you have purchased TetraPond bio activators, it will pass through these. It is here that beneficial bacteria convert harmful nitrites to nitrates.

Aquatic plants will absorb most of the nitrates. The cleaned water is then expelled through the ridged spillway.

The TetraPond waterfall filter offers both mechanical and biological filtration. It will support pumps of between 500 and 4500 gallons per hour.

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CNZ ALL IN ONE Pond Filter System with 13W Sterilizer 660GPH Pump Fountain Kits

If you have a small to medium-size pond, the CNZ filter system is a good choice for your garden. The integrated filter and pump system will support a pond of around 1,000 gallons of water. In addition, it is designed for submerged installation.

The filter includes three fountain attachments so you can customize your water feature. Alternatively, you can divert the water to create a waterfall. The fountain and diversion splitter have flow rate controllers. This gives you complete control over the fountain water pressure.

The CNZ is a single and smart unit that is easy to install. It comprises both a filter and pump, offering a flow rate of 660 gallons per hour. The system has a sizeable coarse filter through which the water enters. Three filter media baskets follow. For maintenance and cleaning, unclip the lid using the clips on opposite sides of the unit.

The built-in 13-watt UV sterilizing lamp takes care of algae and other unwanted microbes.

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Aquagarden Water Pump for Ponds | Submersible Water Pump

The Aquagarden water pump combines a filter and a pump. It is designed for ponds of up to 600 gallons. It includes a fountain connection with three fountain heads and an LED spotlight for the fountain. The adjustable fountain will reach heights of up to four feet.

The Aquagarden water pump and filter are designed for submersion. Pond water enters through the top grill, and the top foam filter sieves out larger debris particles. A second padded filter removes smaller particles. The water then passes through an even finer polymer wool filter before dropping onto the ceramic bricks. The ceramic bricks provide the media upon which the beneficial bacteria grow. As a result, bacteria settle upon the bricks, clearing toxins from the water.

The unit has a built-in UV light which is equipped with an automatic safety switch. A locking handle ensures easy removal from the pond. The filter/pump system has a two-year warranty.

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Buyer’s Guide

Filtration Stages

Koi pond filters all have two stages, mechanical filtration, and biological filtration. Each is equally important to ensure clear, healthy water.

Mechanical Filtration

The mechanical filtration system ensures that your pond water stays clear of debris. It sieves bits of food and other solids through a physical filter. The best filters have multiple filter layers to filter out different-sized debris without clogging it up.

Biological Filtration

Mechanical filtration should leave your water clear, but toxins may lurk in the clearest of water. It is the job of the biological filter to clear the toxins. A good biological filter should remove ammonia and any unwelcome microbes from the water.

Biological filters typically use substrates that aid the growth of microorganisms. These microbes transform toxic waste like nitrites and ammonia into nitrates that the pond plants absorb. This filter also encourages the development of similar beneficial microbes on the rocks in the pool, so they, too, will assist in clearing toxins from the water.

To properly clean the water, beneficial bacteria in the filter need a large surface area and a decent water flow.

Ultraviolet light in the pump can take care of bacteria and parasites to not infect the fish. However, for the UV light to work effectively, the water must be clear. Water must also not pass through the filter too quickly.

How Much Filtration is Necessary?

The amount of filtration you need will depend on the size of your pond and what you have living in it. All filters are rated for pond water volume. If you have koi in the pond, this will increase the required filtration to clear the food and waste residues they create.

Depending on the population density of your koi, you need a filter that is between two and four times the rated capacity for the volume of your pool. If you have any doubts about the size, you need instead buy bigger.

So, if you have a koi pond that contains 1,000 gallons of water, you should buy at least a 2,000-gallon filter. If your pond is in the sun or the population density is high, you should double that.

Pressurized vs. Non-Pressurized Filters

Pressurized and non-pressurized filters both have their advantages and drawbacks. You’ll have to weigh up the pros and cons when making the decision on which to buy.

Pressurized Filters

Pressurized koi tanks, or bead tanks, can process large volumes of water. You can install them either below or above ground.

The movement of water through these systems is much slower. The result is more effective filtration because the water is in the system for longer. The problem is that the beneficial microbes needed to clear toxins and convert ammonia do not thrive in these conditions because of the limited oxygen supply. Again, this is due to the slow flow of water through the system.

This is usually only a problem where there are large populations of koi in the pond. You can overcome the problem by adding a pre-filter or introducing air into your filtration system.

Pressurized filtration systems are typically more expensive than non-pressurized systems.

Non-Pressurized Filters

Box filtration, or non-pressurized filtration systems, avoid some of the problems of the pressurized units. Waterflow into the box filter is not impeded in any way, so the bacteria that live in the media have plenty of oxygen and should thrive.

A good box filtration system should remove debris as effectively as the more expensive pressurized filters. Most filters have several filter layers in the mechanical filter to remove particles of different sizes without clogging up. Many box filters also include UV lights to eradicate algae and other microbial contaminants.

If you have a well-stocked koi pond, consider installing a box filter ahead of your pressurized filter to offer additional biological filtration.

Setting Up a Koi Pond Filter System

Rather than buying a filter system, you may choose instead to build your own.

You will need:

  • A 5-gallon bucket with a sealable lid
  • A water pump rated for your pool size
  • Enough hose to run from the pump to the filter and from the filter to the pond
  • Red lava rock
  • Filter material or a laundry bag containing kitchen sponges


  1. Cut a hole in the lid of the sealable container for the hose.
  2. Cut a hole in the side of the bucket about an inch from the base for the outlet pipe.
  3. Insert the hose into the holes and seal the holes with an aquatic-grade sealant.
  4. Place the red lava rock into the bottom of the bucket, high enough to cover the hole at the base.
  5. Cut your filter material so it fits snugly into the bucket.
  6. Place several layers of filter material over the lava rocks. You may need to place a layer of metal screening beneath so that the filter material lies flat.
  7. If you’re using a bag of sponges, make sure that the bag completely covers the rocks below.
  8. Place the lid onto the container and seal it.
  9. Install the filter.
  10. Using the same sealant you used to plug the hose holes, attach a screen to your input hose to prevent large particles from entering your filter.
  11. Connect the pipe from your bucket lid to the pump outlet.
  12. Place the filter outlet hose into the water. Make sure that it is as far from the pump inlet as possible.
  13. Plug in the pump and switch it on.

If water doesn’t run out through the filter outlet pipe after a few minutes, your lava rocks may have blocked the outlet.


What Size Pump Do I Need for My Koi Filter?

The purpose of the pump is to supply water to the filter for cleaning. So, the two must be well-matched. To choose the right size pump, you will have to calculate how much water you have to move. Depending on the size of your pool, you should aim to move the water through the filter every two hours. If your pool is heavily stocked, increase the rate of flow through to once every hour.

Koi produce about four times the waste as typical pond fish. Therefore, the size of your koi population is an essential factor in deciding what size filter and pump you need.

How Often Should I Clear My Filtration System?

How often you need to clear your mechanical filter box will depend on how many koi you have in your pond. Rule of thumb – once a week should do it. Watch your filter outflow. If there is a reduction in water flow or pressure, the filter needs cleaning.

Pond filters have mechanical and biological filter systems. Mechanical filter clears out solid waste, and biological filters use beneficial bacteria to change toxic waste into less harmful nitrates. However, if too much sludge is allowed to collect in the mechanical filter, it will slow the flow and start to break down, creating phosphates.

Can You Put Too Much Oxygen Into A Koi Pond?

It is improbable that you could put too much oxygen into the water. However, it is possible to create supersaturation in a pool which will harm your fish; however, this can only happen if oxygen is forced into the pool under pressure. This situation is possible in the unlikely event that the pipe leading into the pump develops a pinhole and sucks air into the pool.

It is more likely that you have insufficient air in your pond. Air is added via the pump and aquatic plants that create oxygen. Pond owners may try to overcome problems of under-oxygenation by pumping more oxygen into the pool. This will add bubbles. Excess oxygen will evaporate.


A garden pond stocked with koi is a lovely addition to any garden, but these bright and colorful fish require clear clean water. This is, after all, their living space.

In addition, leftover food particles and waste will collect in the water in the absence of an efficient and effective filtration and pump system.

A good pump will clear debris. It will also promote the growth and colonization of beneficial bacteria to convert ammonia and nitrites to nitrates. Add a UV light for the eradication of free-floating algae and unwanted microbes.

This combination of pond filtration will ensure that your koi remain healthy and free from disease and your pond water crystal clear.