Koi Pond Filtration

How to Keep the Koi Pond Clear

Koi are active creatures that like their food and scavenge for it. When active they eat a lot and like to explore every level of their environment/habitat from top to bottom while producing a lot of waste. So it’s easy for the koi pond to get dirty/murky quickly when not cared for. Koi pond filtration helps Maintain a clean and healthy koi pond which is essential for the optimal health and growth of the Koi while enhancing and preserving the aesthetic appeal of the pond. There are various factors that can affect and alter the koi pond environment.

Overcrowding & Overfeeding

Koi themselves are known to grow large easily, a general rule is per inch of fish should be accommodated by 10 gallons of water a 10-inch fish would need around 100 gallons of water and if overpopulated it can lead to excessive waste and can cause an imbalance in the tank.

Koi feeding patterns are different during different seasons, during winter they mostly go without food or by sustaining on algae or micro-organisms, while during summer if overfed they can cause excessive waste and contaminate the koi pond easily.

Excessive Live Plants

Adding live plants adds to the aesthetic appeal and also enhances the environment for the fish making it a more fish-friendly habitat. However, the water to plants ratio should be around 60-40/50-50, adding excessive live plants can block the natural sunlight from reaching the bottom of the surface and block the fish from accessing essential dissolved oxygen available on the surface. Also, Koi like to pick on live plants for feeding & scattering around the debris.


The whole koi pond water needs to be circulated at least once every hour. Check for any debris blocking the flow of the water & make sure that the amount of water flow isn’t higher than the pumps flow limitations.

Koi Pond Filtration

Koi pond filtration helps in keeping the pond clear & maintaining a healthy environment. Any built-up waste or debris could cause a toxic environment in the pond. Mechanical filters help in removing any debris on the surface like sticks and leaves.

The biological filters can be used to create a waterfall in the pond; they essentially use bacteria to break down the waste in the pond into less harmful substrates which could be consumed by aquatic plants.

Algae Check

Algae overgrowth can build up sludge/slime at the end of the tank, though Koi occasionally feed on algae too many algae can deprive koi of oxygen. Algae feed on the nitrate produced from ammonia during the filtration for their growth. Treat the pond for algae if necessary while a pond vacuum can be used to suck any sludge/slime present at the bottom.


Stagnant water can cause the growth of algae & bacteria which can suck up the oxygen necessary for fish. Aeration can help with the water flow & in maintaining the levels of dissolved oxygen in the water essential for fish & plants.

Water Change

The water level of the koi pond reduces naturally due to evaporation. Normally 1/2inch of water would be reduced every day, if there is a sudden decrease in the water level check for any possible pond leaks. If possible change around 10-15% of the pond water every week and replace it with fresh water &dechlorinate it if necessary.



Regular Checks

Regularly check the koi pond for any debris forming up and try to clear it up using the pond net, any decay can damage the water.

Seasonal Maintenance


As winter approaches Koi will start eating less and eventually feed on their own resources for energy. Clean the filters every month throughout the winter.

  • Due to the low-temperature thick ice sheets may form on top of the pond’s water surface which can limit the oxygen flow to the fish, making a hole in the sheets can help with the oxygen flow, a “De-Icer” can also be used for this purpose.
  • A heater can also be used to regulate the temperature if needed.


As spring comes the fish slowly start eating again and start producing waste. Clean the filters and clear up the debris. Reinstall any equipment which was removed due to the weather in winter. As the Koi immune system can be vulnerable during spring check for any signs of illness.


Summer is the time when the Koi activity is at its peak capacity. The high water temperature makes it active & also increases the metabolic rate, so the fish binge on food and also produce a lot of waste.

This is also the time when bacteria and algae growth spike up. Regularly clean the filters and do not let any debris build-up. Feed the fish 4-5 times a day(dependent on the fish).

If the water temp goes above 75*F fish might find it hard to adjust to it so adding aquatic plants for shade might help or an aerator too can provide the fish with sufficient dissolved oxygen.


A lot of debris like leaves, twigs & sticks are seen in the fall. Consider getting a net if the pond is directly below the tree. Filters need to be washed and cleaned thoroughly as any stuck-up debris can hinder their functionality. Remove any sludge buildup at the bottom as it helps in preparing the pond for winter.

Essentially clean the filters and change some of the pond water every week if possible. Do not let the debris build-up and decay & do not overfeed the fish. Check the water temperature regularly. If the equipment is taken care of properly it will do most of the job and reduce the stress.