How Often Should I Change My Koi Pond Water?

Suppose you have a new koi pond, and you’ve noticed that it is getting increasingly harder to see your koi fish due to the water being so murky. In that case, you may be wondering whether you need to change your water and if changing your pond water should be part of your pond’s regular maintenance. 

It would help to aim for 10–20% pond water exchanges every week. Changing small amounts of water weekly is less stressful for your koi than large amounts changed monthly or bi-annually. Changing your pond water is vital to ensuring your koi grow properly and remain healthy. 

If you want to keep your koi healthy, 10-20% water change per week is acceptable if your pond has over 5000 gallons of water. If you wish to grow your koi to their full potential in size and vibrancy, 10% water change per day is recommended.

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Why Should Koi Pond Water Be Changed?

Changing your koi pond water is a vital part of your pond’s routine maintenance. If you have not changed your pond’s water in a while, there will be a build-up of nitrates and ammonia in the pond water. This build-up can pollute your pond and be hazardous for your koi fish.

As many professional koi farmers know, the main reason for the disease and death of fish in your pond is polluted water. This is why it is essential to maintain good water quality by changing out polluted water weekly.

A water change is only considered a water change if dirty water is removed from the pond before clean water is put in. If you are filling up your pond with hose water every week to compensate for evaporation but not removing any of the old water, this is not considered a water change as no pollutants were removed from your pond.

As chlorine is toxic to your fish and specific water plants, and the bio-organisms in your pond, you will need to treat any tap water with chlorine remover before filling up your pond with clean water. 

Water changes are essential for keeping your koi healthy. If you neglect to change your pond water regularly, there will be a build-up of pheromones and toxic chemicals that are dangerous for your fish. 

How Often Should Koi Pond Water Be Changed?

It would be best to try a weekly water exchange of 10-20% for your pond water to remain high quality and your fish to stay healthy. Changing small amounts of pond water regularly puts less stress on your koi fish than significant, infrequent water changes.

For smaller ponds with less than 5000 gallons of water, you’ll want to change around 15% of the water. Smaller ponds with more fish have less water, and therefore the water quality degrades quicker due to the higher density of pollutants in the pond water.

For larger koi ponds, with over 5000 gallons of water, you can stick to a 10% change in water every week. For smaller ponds that do not have many koi fish, a 10% water change every week is still acceptable. 

For larger ponds that do not have many koi fish, a 5% weekly water exchange will be appropriate for the number of pollutants in the water. Ponds with heavy bio-loads should have higher amounts of water changed more frequently. Some koi owners change their water daily via a drip mechanism or trickle filters.

How To Change Koi Pond Water

Depending on what size pond you have and the available equipment, there are different ways to change your pond water. 

Smaller Koi Ponds

For smaller koi ponds, you should be able to use either a siphon or a pump to remove the excess water out of your pond. You must remember standard tap water contains both chloramines and chlorine, which will be toxic to your koi fish and water plants.

You need to use a water conditioner and other water treatment products to strip the tap water of the existing chlorine and contaminants. To change your pond water, siphon or pump the amount of existing pond water out into containers or your garden.

Next, you can add the water conditioner and water treatment products to your pond water. Once you have done this, you can begin refilling your pond with tap water from a hose. You will need to watch the water level to ensure your koi pond does not flood.

Treating Water Before Adding It To The Koi Pond

This method is the safest and easiest method for your koi fish. Pre-treating the tap water will ensure it is safe before reaching your koi fish. With this method, you can still use your pump, siphon, or even a pond vacuum. 

For this step, you will need to know how much water you will need to put back into your pond after removing the polluted water. Use buckets or containers and fill them will tap water. Pour your treatment products into the buckets and leave them to stand for 12-24 hours. This will ensure that all the chemicals and chlorine have dissipated.

Once your treated water is ready to go, remove the polluted water from your pond and into a container so you can keep an eye on how much water is being removed. Once the necessary amount of old water is out, you can start refilling the pond with clean, treated tap water.

Long Term Water Changing: Drip Mechanisms / Trickle Filters

Drip mechanisms and trickle filters are the easiest ways to change your pond water over a long period regularly. The downside is it will take a while to install, and it can be pretty costly. 

The first thing you will require is an overflow drain. An overflow drain is a device that will allow any excess water to flow out of the pond once the pond water has reached a certain level. After you have installed your overflow drain, you will need to install a permanent water line to ensure that new water is constantly flowing into the pond.

You will need a drip mechanism or a trickle filter to slow down the flow of water coming in. With this equipment, you can change 5-15% of the water every week through tiny constant daily changes in water instead of one large amount being changed. 


To keep your pond and your koi fish as healthy as possible, you will need to change roughly 10% of the pond water weekly, depending on the size of your pond and the amount of koi you have. 

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