Oxygen in the pond water plays an important role in the Koi pond since an excessive decrease in the oxygen concentration can be fatal for the animals. The optimal content of oxygen in the pond water for Koi is 6 mg / l. 

This value is determined by the water temperature and the stress resistance of the animals. The breathing of the fish is adapted to the rather low oxygen value of the water. Koi have a low body temperature, it is in the same range as water temperature. If the water temperature rises, the fish need it for their metabolism also more oxygen. However, since the oxygen saturation of the water decreases more and more with increasing temperature, this results in the ideal oxygen concentration value and a maximum temperature at which the Koi can live.

Caution is advised if the oxygen concentration in the pond water falls below 5 mg / l. After a while, the animals begin to get the lack of oxygen on the surface of the water and there gasp for air. This behaviour is known as wheezing. This remarkable behaviour can also often be observed at waterfalls since the oxygen concentration is also lower here.

For a short period of time, values ​​between 4 mg / l and 5 mg / l can be tolerated; in the long run, such a low value is alarming. When the oxygen level drops to 3 mg / l, the koi usually die. If such a sharp drop occurs, action must be taken immediately.

It is therefore advisable to regularly check the oxygen content in the pond water

The oxygen content should be monitored, especially at high outside temperatures and if there are problems with the water quality of the Koi pond or the pond technology. Either an electronic measuring system can be used here, which causes higher acquisition costs, but is profitable over the years and enables easy reading and accurate values. 

Commercially available powder and drop tests are a popular alternative to check how much oxygen there is in the pond water. After a three-step measuring process, the value can be read off using a colour scale. Caution is advised when adding chemicals to the pond water, they can falsify the measurement results of these tests.