Always dechlorinate any tap water that you use to refill your pond.

Clear away any extra debris from the surface of the koi pond with a skimmer net.

You can buy containers of beneficial bacteria online from shops specializing in aquatics.

Keep in mind a complete clean of the pond could interfere with algae growth in the pond. But if your koi pond is really dirty from the winter or from poor maintenance, you may want to use a vacuum for a more thorough clean.

You can do a fall cleaning if you are not able to clean the pond during the spring. In the fall, your pond may become full of fallen leaves and debris as the trees change, so you may think about doing a clean. However, you should try to maintain the koi pond during the spring, summer, and fall so the once a year clean is easier to do. [9] X Research source

As you pump out the water, make sure you leave about one foot of water at the bottom of the pond so your fish can swim around. You can then leave your koi in the pond as you wash the pond and clean out any debris. You may decide to leave the koi in the pond if your pond is large and you do not want to deal with taking out all the koi. If you decide to remove your koi from the pond, you should pump out about one foot of water into the holding container meant for your fish. This way, you can transfer the fish into the container in water that they are used to swimming in to avoid shocking them. You don’t need to drain the pond every year to clean it. [13] X Research source Clark Hill. Plant Specialist & VP of Operations, Platt Hill Nursery.

Use the skimmer net to scoop the koi out and place them gently in the holding container of pond water. Once you have all the koi in the container, you should cover the container with netting or a breathable lid so the koi do not jump out. [15] X Research source Place the container in a shaded area in your yard, away from sunlight. This will ensure the koi stay healthy and happy while you clean the pond.

You should also take out all water accessories in the pond, like water plants or water features. You can then place the plants in a shaded area of your yard and cover them with newspaper to protect them. You should place underwater plants in a container of clean water. If you have any water features in your pond that are made of non-natural materials, such as plastic items, you can use a toothbrush to scrub and clean them so they are ready to go back into the pond once it is clean. [18] X Research source

Use the hose to wash any other attached features on the pond, such as a waterfall or rocks around the perimeter of the pond. Never use any chemicals to clean the pond, only water, as chemicals can introduce toxic substances into the pond environment. You can then use the pond vacuum to remove any sludge at the bottom of the pond that is hard to get out with the hose. You may come across very smelly goo, decomposed plants, or even a dead frog or fish. Remove it all so the pond is free of any bad bacteria or debris. The sludge on the bottom of your pond does contain beneficial bacteria, so you don’t need to remover it completely. [21] X Research source Clark Hill. Plant Specialist & VP of Operations, Platt Hill Nursery.

If you have water plants, you may wait until you fill the pond with new water to place them back in the pond.

Once the pond is filled with new water, add the dechlorinator to the water to remove the chlorine in the water. Turn on the pond pump and allow the water to circulate in the pond for five to ten minutes. [23] X Research source To avoid shocking your fish, you should dump some of the water from the holding container and replace it with the new pond water. Do this several times to allow your koi to get used to the new water. The fresh water will be colder than the water your fish are used to and exposing them to water can shock them. [24] X Research source

If you did not remove your koi from the pond, you can skip this step.