How Do I Keep The Water In My Koi Pond Clear?

When you dreamed that elegant koi pond into existence to make your garden into a peaceful haven, the image in your mind must have been of crystal clear water, graceful koi gliding by, and picture-perfect pond plants. But at some point, every pond-owner is faced with the reality of a murky or green pond. How do we keep it clean and clear?

Regular maintenance of a koi pond is of the utmost importance for keeping the water clear. It involves maintaining your fish population, the plants in the pond, the filtration system, and the regular removal of debris. If the pond still turns green, there are natural ways to remove the algae.

Good quality water places a vital role in keeping your koi pond clean and clear, which will have a direct effect on the health of your koi. Sometimes your water may even appear clear, but you notice your fish behaving differently, which means there is something wrong with the water.

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How To Keep Koi Pond Water Clear

Maintaining clear water is much easier than trying to clean it when it already looks like pea soup, so a little regular effort will help keep your pond and fish healthy. Here are some pointers to help avoid the pea soup scenario.

Keep A Healthy Koi/Water Ratio

If there is too many koi fish in your pond, the excess fish waste can upset the balance of your pond water. You shouldn’t have more than 10” of fish per 100 gallons of water. That may be hard to quantify, but if the water is murky or green and the fish seem to play bumper boats with each other, it’s time for some of them to move house.

Feeding The Koi Correctly

It is important not to over-feed the koi as the food leftover will sink to the bottom of the pond and decay. It would be best to feed the koi good quality food once a day, giving them only what they can finish in 2-3 minutes. The best food floats instead of sinking to the bottom if not eaten.

The Koi Pond Needs The Correct Balance Of Plants

At the height of the summer, 40%-60% of the koi pond’s surface should be shaded or covered by plants. Too many plants can starve the fish of oxygen at night due to taking in oxygen and giving off carbon dioxide, i.e., photosynthesis.

A Koi Pond Needs The Right Size Pump

When setting up your koi pondchoose a pump that can circulate all the water at least once per hour. Check that the pump’s flow isn’t inhibited by debris stuck in the biological filter or the skimmer.

Clean The Koi Pond Manually Before Debris Can Decay

A pond skimmer will do most of the debris removal for you, but fishing out dead leaves and sticks with a net before they fall to the bottom and rot will help keep the water clean. Decaying debris, fish waste, and excess fish food can cause ammonia levels to rise, which can be harmful to your fish. If they are jumping out of the water, they are not doing tricks. Your pond needs a neutralizer.

Choose A Good Filtration System For Your Koi Pond

It’s a good idea to choose a filter that can manage more than the capacity of the pond and clean it regularly according to the manufacturer’s instructions. There are two main types of filters. Skimmers remove the debris from the surface of the pond water. Biological filters use bacteria to break down the waste into less damaging compounds that the pond plants can absorb.

Keep The Pond Cool In Summer

The water temperature should not exceed 75°F because it causes a loss of oxygen in the water, which is detrimental to the health of your fish. If the fish are coming to the surface for air, an aerator will help during extreme heat. 

What To Do If The Koi Pond Is Murky Or Green

Green koi pond water

Excess biomass and algae can ruin your mental image of the perfect water garden very quickly, but once it’s happened, most of us don’t like to use toxic chemicals to fix the situation. There are a few options that don’t include chemicals.

Use Barley Straw To Get Rid Of Algae In Your Koi Pond

Algae makes the pond look horrible, hides your beautiful koi, and is harmful to them. If the algae are left to grow, it will eventually starve the fish of oxygen. 

Barley straw is a cheap and natural algae killer and won’t pose any danger to the koi or the plants. It is available in small bales from garden centers. You can tie mesh packaging around a small bunch of straw and connect it to an area where the water can flow through it. It releases a chemical similar to hydrogen peroxide, which kills the algae over time as it decomposes.

Full Cleaning Of A Koi Pond

A more drastic method of returning the pond to its former glory is to drain it completely. First, transfer the fish into a bucket of pond water. Capture them in a mesh net because nylon nets are abrasive. You can place an aerator in the bucket while you clean the pond.

Use the pump to drain the pond water and clean it as fast as possible with a hard scrubbing brush or toilet brush (new). You can also spray the rocks with a high-pressure hose to remove the remaining algae. Then quickly refill the pond and return the fish to their cleaned home.

DIY Quilt-Batting Filter For The Koi Pond

This cleaning method from the pond can work within a couple of hours for a small pond but can take much longer for more extensive ponds. 

Find a waterproof container, like a milk crate, with holes in the sides. Attach a hose to the pond pump so the water can flow out of the crate. Put the pump inside the crate and cover all the sides with polyester quilt batting. The hose must protrude into the pond. The quilt batting will catch the dirt and algae and eventually turn green or brown, and the water will ultimately clear.


A Koi pond is a beautiful asset to your garden and easily managed. The water can stay clear if you do regular maintenance before the algae has a chance to get out of hand or debris decays on the bottom. Just keep at it. 

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