Koi Ponds Tips – Water Chemistry and Oxygen Levels

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Water quality is a significant factor in creating an ideal condition for the inhabitants of a koi pond. The condition of the water in the pond strongly influences the koi’s health and well-being. Poor water quality paves the way for various health problems that can endanger the pond inhabitants. With proper care and foresight, these problems can be avoided.

To ensure that your pond’s aquatic habitat is a perfect place for your koi and aquatic plants, it is best to know more about these important water parameters and how to keep them at recommended levels.


For koi, the ideal level of oxygen dissolved in water should be at a minimum of 5 mg/litre. Keep in mind that cold water can hold higher levels of dissolved oxygen compared to warmer water. Thus lower levels of dissolved oxygen are likely to occur during the warm summer days. Overcrowding in the koi pond can also lead to higher dissolved oxygen in the water.

There are several ways for oxygen to become dissolved in the koi pond. These include surface diffusion of oxygen from the atmosphere or an airstone on the pond’s bottom. A fountain or waterfall also increases the agitation of the water surface to generate dissolved oxygen.

Water pH

The pH value reflects the degree of acidity and alkalinity of a substance. In koi ponds, a change in pH can definitely affect the fish in negative ways. The ideal pH of a koi pond is between 6.8 and 8.2. You should monitor the pH regularly using test kits and be quick to address any pH fluctuation as soon as possible.? The use of hardness or buffers can help stabilize the pH levels of the pond.

Ammonia, Nitrates, and Nitrites

Ammonia is the waste material excreted by fish. Bacteria in the water can break down ammonia to nitrites which can be further broken down into nitrates and, eventually, free nitrogen. When these compounds are not kept in check, they can give rise to various health problems that can be fatal.

High levels of ammonia can damage your fish’s gills and reduce the ability to utilize dissolved oxygen in the water. High amounts of nitrites can damage the kidneys and nervous system, while high levels of nitrates can compromise your fish’s immune system.

As a rule, ammonia and nitrite levels should be zero. A reading of 20-60 ppm for nitrates is acceptable as long as it can be addressed as soon as possible.


Higher temperatures can worsen existing problems in the pond. Warm water holds less dissolved oxygen and is favourable for increased levels of toxic ammonia.

More tips to keep your pond healthy

Frequent partial water changes are a must. Changing at least 10% per week will help ensure that water parameters won’t undergo rapid fluctuations and stress your koi.

If there are aquatic plants in the pond, provide lots of oxygen. Also, remember that large koi require more oxygen than smaller ones.

Be sure to use a good de-chlorinator to neutralize chlorine or chloramines during every water change.

Monitoring pond water temperature, pH, ammonia and nitrite using commercially available test kits should be done every week.

Filters should run 24/7

Pond filters need to be cleaned at least once a week during summer and once a month during spring and fall.

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