Pond Filters

If your pond pump is the heart of your pond, your pond filters are like the lungs, filtering the impurities and toxins out of your pond. Getting pond filtration right is critical to maintaining a healthy sparkling pond.

Optimal water quality is essential to the health of your koi pond. Not only is sparkling clear water important for the health of your fish, it also more beautiful to look through when viewing your fish.

There are two secrets to sparkling pond water. You will be amazed at how easy this is.

• You will need a large over-capacity biological and mechanical filtering system.
• You need to plan ahead for easy cleaning and maintenance of the filter system. Easy cleaning means that you will clean it more often. So, ease of use is important consideration.

There are three kinds of pond filters to choose from.

Biological Filters

Biological filters promote surface area for good bacteria to grow on while breaking down the organic matter that is given off by plants and fish waste. These fish pond filters help break down the ammonia and other waste.

Plants can be used as a “vegetation filter” to help prevent algae from getting a hold.



Think about it like this: More plants equals less algae. Use plants that get a good foothold before the algae do. A good biological filter can get a bacteria colony started in as little as 2 weeks. Making a biological pond filter is not hard to do. The materials are readily available from your Home Depot store.

The simplest and best bio pond filter system I have found after spending mega time and money experimenting is a lava rock filter system.

We will show you how to build your own pond filter using a livestock tank - it is easy and cheap.

Another biological filter to help control algae is barley straw. We use small bales of this in our horse water tanks to control the algae there.

Mechanical Filters

Mechanical filters physically remove particulates from the water – but not the algae. These filters do not remove the ammonia and fish waste – so with these types of filters you can still get green water.

You will want to consider adding a pond skimmer to your pond to help keep the leaves, floating algae, and other large organic waste from falling to the bottom of the pond and decaying. We will show you an easy way to build a pond skimmer.

Chemical Filters

Chemical filters require adding chemicals to the water to “kill” algae. I do not recommend this type of filter. If you are killing the algae, there is no telling what else you are killing. You will always want to be cautious about what you add to your pond that may kill your plants or fish. Best to stay way from these chemicals if possible.

Ultraviolet lights can be considered “chemical” filters. Their benefit is that they also kill pathogens that may cause fish infections.

When building your pond, you should consider adding an under-gravel filter. They are cheap and easy to build, and will help with the circulation of the water and filtration of the fish wastes that drop to the gravel.

Cleaning your Filter

You should clean your koi pond filter at least once every ten days in the summer when your fish are active. If you have built this filter according the specifications here, this should take you less than one hour to do. If you have a garden, drain the filter there. The plants will love the wastes and it provides free and cheap fertilizer. To clean, just shut off the pump and drain the filter. Wash your koi pond filters out with a water hose – do not use the sprayer. You just want to flush the filter material out until the water runs clear. Then reassemble and fill back up with water.



Your pond may get cloudy immediately after flushing the filter, but it will clear up quickly.

I use a combination of biological and mechanical filtering in my ponds. I tend to avoid chemical filters, but I do use ultraviolet to help control pathogens.

Your pond filtration system is the most important component of ensuring you have a sparking backyard garden koi pond. If you get this right, you will have hours of enjoyable time with your koi pond.

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