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Koi keeping is keeping water quality

written by Hugo J. Smal

Kim Young Soo and I are each moment of the day busy with the water quality in the Koi house. We are sure: Keeping Koi is keeping water quality. We do not measure it many times but looking thoroughly.
What is the colour of the water? Is the surface not hollow? Is the water appearing natural or a little chemical? Next to that that we are looking at the skin of the Nishikigoi. The shiroji (white skin) must be white. If there is a red, burnt like colour, most of the time something is wrong with the water.
Yes, we look at the water but maybe it’s better to measure regular. Together we have much Koi experience and the Koihouse is our home and the ponds our rooms. But surely we advise you to measure your pond water.

A Koi can only reach its full quality if the water quality in which it swims is optimal throughout its entire life. Certainly, everyone who has Koi must be aware of this at every moment of the day.

The composition of water is very important. In the pond, there are constant interactions between chemical and biological processes. To be able to control these properly, it is important to understand the various main players in these processes. I’ll list them.


Koi can live in water temperatures between about 4 and 32 degrees Celsius. Large fluctuations in short periods disturb the digestion and all kinds of other processes in the body of the fish and lead to stress. Keep in mind: stress often leads to illness. Getting used to a different temperature should be done as gradually as possible. As guidance; Bridging a maximum of five degrees (gradually) upwards per day and a maximum of two degrees downwards.

Oxygen (O2)

Oxygen is necessary for the conversion of fuel into energy. Fuel + Oxygen (O2) form Energy, Carbon Dioxide (CO2) and Waste. To make this combustion (oxidation) possible, a sufficient level of oxygen is necessary.
Oxygen is also important for the filter bacteria to do their job. Please note that these bacteria are not only in the filter but also attach themselves for example to the pond wall. Hot water may contain less oxygen than cold water. Therefore, you have to aerate your pond and filter sufficiently. This certainly during the warm months of the month. Keep in mind that there is never too much oxygen.
Oxygen is measured in absolute value (milligrams per litre or parts per million (ppm)) and in relative value (per cent saturation at a given temperature). The absolute value is important to control the minimum amount of oxygen. For carp, this is around 5.5 milligrams (5.5 ppm) per litre. The relative value makes the oxygen content comparable over a longer period and says something about the effectiveness of your system.

Ammonia (NH3)

In addition to energy, the combustion of food also creates waste. This waste ends up in the pond environment in the form of faeces (organic pollution) and is broken down by bacteria into ammonium. A large part of the waste (up to 75%) enters the water as ammonium via the gills of the fish.
Depending on the acidity, some of the ammonium forms into ammonia. Ammonia is an extremely toxic gas dissolved in water. Ammonia is already harmful at 0.1 milligrams per litre (0.1 ppm). The higher the pH (acidity), the more ammonia is formed! This also applies to the temperature. The higher the temperature, the more ammonia is formed!

Nitrite (NO2)

Fortunately, some bacteria convert ammonium/ammonia into nitrite. A good biological filter does its job. One problem: Nitrite is also poisonous. Fortunately, other bacteria convert the nitrite into the more or less harmless nitrate (NO3). Nitrite at 0.2 milligrams per litre (0.2 ppm) is already harmful in the long term. The lower the pH (acidity), the more toxic nitrite becomes!

Acidity (pH)

The pH of a Koi pond should be between 7.0 and 8.0. An acidity below 5.0 and above 10.0 is deadly. Strong fluctuations are also not good for Koi. Koi can not tolerate strong fluctuations in pH. Rather a stable pH of 8.2, for example, than fluctuations between 7.0 and 8.0. The pH scale is logarithmic, which means that a pH 5 is ten times more acidic than a pH 6, and 100 times more acidic than pH 7!

Carbonate hardness (KH)

The KH is also called the buffer of the pH. The KH stabilizes the pH. The KH is expressed in degrees DH and measures the number of bicarbonates in the water. Acid (H +) is continuously formed by the conversion of ammonia and nitrite into nitrate. Acid can also get into the pond through rain and decomposition processes of organic material. So you would expect the pH to drop to dangerous depths. However, the bicarbonates (HCO3-) in the water neutralize the acid (H +), preventing a drop in pH.
When the KH is been “used up”, there is a danger that the pH will drop to dangerous depths (pH crash)! It is therefore important to have KH between 6 and degrees.

Goyang Koi: Koi keeping is keeping water quality

Yes, these are the protagonists and you have to keep an eye on them all. If something goes wrong, everything will fluctuate. There are all kinds of products for sale with which you can make adjustments. We at the Goyang Koi farm are not in favour of this. When the pond is properly constructed, a good filter does its job and the water with which you refresh has the correct values, then changing water is always better.

We are convedant in supplying you his kind of information. When you have a nice Koi hobby we at the Goyang Koifarm are very happy. If you have any questions about the hobby contact us or use the contact form.

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