Koi Ponds Tips – Water Chemistry and Oxygen Levels

Water quality is a very important 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.

In order 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/liter. Keep in mind though 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 water.

Waterfall aerating a koi pondThere are several ways for oxygen to become dissolved in the koi pond. These include surface diffusion of oxygen form the atmosphere or by placing an airstone on the bottom of the pond. 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 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 the levels of these compounds are not kept in check, these 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 the immune system of your fish.

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 favorable 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 dechlorinator to neutralize chlorine or chloramines during every water change.

Monitoring of pond water temperature, pH, ammonia and nitrite using commercially available test kits should be done on a weekly basis.

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.

About the Author:

This is a guest post by Peter Hartono. Peter is an aquarium hobbyist and fish pet lover who devoted his life in producing home-grown aquatic plants. He is also the founder of Just Aquatic, a proud Australian company and retailer of a wide range of aquarium supplies including Zoo Med, BiOrb and Exo Terra.

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