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How to Keep Koi Pond Water Clear

| Updated September 26, 2017

Koi are a show fish and clean water is ideal for viewing their unique color patterns and movements. Keeping your koi pond clear is possible using a regular cleaning schedule and several tools to move and filter the water. The methods of cleaning are similar for indoor and outdoor ponds but indoor ponds are much easier to maintain.

Causes of Dirty Water

Dirty water is caused by the accumulation of food, feces and biomass from the environment. Decomposing leaves, dirt and organic material will reach your pond, especially in the outdoors. While organic material is healthy to a degree, you must limit the stagnant nature of your pond and cycle water through filters and aerators.

Bottom Substrate

Stabilize the bottom of your pond with solid substrate. Add large rocks and gravel to prevent mud from clouding the water. Mud is not bad for the fish but it does dirty your water. Koi will sit in mud and fan it with their tails. This is good for their skin but it reduces clarity. Do not eliminate mud and silt but limit the amount to keep your water clear.

Manual Cleaning

Manually remove organic buildup from the surface with a seine. Clean the surface several times each week, especially during the fall when leaves are falling off trees. Add leaf netting to your pond if the trees are dense in your area. The netting is inexpensive and captures most of the organic material. This makes manual cleaning much easier as you prepare your pond for the winter months.

Filtration Cleaning

Filters are the key to maintaining clear pond water. Filters cycle the water and remove organic material during the process. Filters are constantly working to keep the water clean. Several different filter options are available. The skimmer is a popular choice because it uses a simple design to efficiently clean the pond. The water flows through a screen that captures debris. You must clean the screen on a regular basis to maintain the filter. The clean water is then pumped back into the pond. Biological filters use a chemical process to convert ammonia buildup from feces to nitrates. This keeps the water clean and healthy for the koi.


  • Use a skimmer and a biological filter in large ponds to tackle dirty water from two angles.

Create Movement

Create movement with a pump or aerator to keep your water active. Oxygen is healthy for the fish and moving the water separates organic material into fine particles that settle quickly settle out of the pond.