Koi crash course - From A to Z

Would you like to look after and advise customers who are koi owners or potential koi owners? Then the best thing you can do is to travel to the Niigata Prefecture in Japan for two months and learn everything you need to know from the koi breeders there, who have learned over generations how to breed, select and care for the world's best koi until they are sold or used again for breeding. Alternatively, you could invest 10 minutes of your time reading this post.

The history of koi

About 2000 years ago, in Japan, the first "colourful carps", which were pretty to look at and were placed in ponds for ornamental purposes, appeared. The first detailed reports on coloured carp, by then called koi, were published in 1870. Through selective breeding and selection, different varieties were created, which were given the Japanese names or descriptive terms now used worldwide (Kohaku, Showa, Utsuri, etc.).

Where are koi bred?

Japan remains the stronghold of koi breeding, even though Israel produced very beautiful koi. In Japan there are three centres of koi breeding: in the north in the Niigata area, in the centre near Hiroshima and in the south near Fukuoka. Are Japanese koi "better" than Israeli koi? A perfect koi can come from Israel as well as from Japan. But in Japan the quality selection is much higher than in Israel. Therefore, generally speaking, the quality of Japanese koi is higher than that of koi from Israel. A koi of medium quality from Japan would qualify as a top koi from Israel. But this is only a rule of thumb. There are, of course, exceptions.

What distinguishes a koi pond from a "normal" garden pond?

Because of the koi's maximum size of about 80 cm, ponds smaller than 15 m3 are completely unsuitable. Most often, koi pond sizes between 30 and 50 m3 are chosen. You cannot cultivate plants in koi ponds, as the koi regard plants as a tasty additional meal. Swamp zones and perimeter planting are possible and indeed beneficial, as plants remove nutrients from the pond water that would otherwise nourish algae. Vertical pond walls offer two advantages, firstly of making more water volume available for the same outline, and secondly making it difficult for herons to eat the koi. 

Watercourses and waterfalls offer the same advantages as in other garden ponds and are often used for koi ponds. Because of the koi's strong metabolism, a bottom drain at the deepest point is highly recommended. The bottom drain is connected directly to the filter and thus prevents larger dirt deposits on the pond bottom. To prevent the drain from clogging, substrates such as gravel should be avoided. A slight slope of the pond bottom towards the drain is advantageous.

Filtering

Koi ponds without filters are like cars without engines. Statements by experienced koi pond builders prove that about 80 % of all "problem ponds" have too small (volume) filters! The water volume of the koi pond needs to be circulated at least once an hour and the volume of the filter chambers should be about 5-10 % of the pond water volume. However, these figures also depend on other factors such as fish stock density, pre-filtering, etc. and can only be used as a guide.

How many koi are allowed in the pond?

This is the most common question and it needs a clear answer. Koi are sociable animals and should always be kept in groups of 10 or more. The rule of thumb is 2000 litres per koi. 

What special pond care do koi need? If you have created a new pond, it is important to observe the nitrogen compounds in the first 3 weeks. After this start-up phase, ammonium (NH4) and nitrite (NO2) must be below the detection limit. Higher values would indicate problems with bacterial decomposition and you would have to postpone the introduction of the koi until the values are correct. The second important point is the pH stability of the water. Minerals in the pond water, called carbonate hardness (KH), ensure there are only small fluctuations in the pH value. Rainwater and algae can dilute or reduce the mineral content and thus lead to strong pH fluctuations. Good products stabilise the pH level and ensure the correct mineral content, especially after periods of heavy rain. Make sure to manually remove heavy accumulations of leaves from the bottom of the pond, as these can block the bottom drain. Removing any organic matter from the pond relieves the filter system.

Are partial water changes really necessary?

Yes - it’s a small investment that brings enormous benefits. Minerals are added to the pond water again and problematic substances are diluted. A monthly partial water change (lowering 15 cm of water as measured from the pond edge) works like a fitness cure for all ponds! Are UV-C water clarifiers advisable? Yes! We recommend them unreservedly as they reduce the germ count and thus the infection pressure on the fish. In addition, good UV-C water clarifiers prevent floating algae (green water).

What’s important when feeding?

Like all carp, koi are omnivores. However, this does not mean that they should be fed on table scraps, but that they MUST be fed a wide range of foods. The key aspect of koi nutrition is adapting to the seasons, as at any given time of the year a certain food composition is the right way to keep koi healthy, prevent disease and get the best colours out of them. A seasonally adapted food is preferable to any food that has only been adapted to the water temperature. Since, for example, the water temperatures are the same in spring and autumn, one might think that the feed composition should also be identical. But this is not the case!

In spring, the animals need to be strengthened after the depriving winter and made fit against diseases such as spring viraemia, while in autumn the koi has to be prepared for the winter and build up reserves. Under no circumstances should koi lovers feed their "normal" food in winter! This can lead to total losses because it can cause intestinal problems if undigested. That’s why a dedicated koi winter food for temperatures between 5 and 10°C is absolutely recommended. As soon as the koi remain quietly at the bottom of the pond and stop their activities, feeding must also stop completely.

Overwintering

Many koi pond owners accept the cost of electricity and use pond heaters to warm their pond water in winter. Some remove their koi from the pond and keep them over winter in indoor facilities/aquariums/mini ponds. The majority of koi owners leave their koi in the koi pond, but take a few measures: an ice preventer, which prevents the water surface from freezing over completely, reinforced by an air pump with a bubble stone.

What should I do if the koi fall ill?

Koi keepers who have accustomed their koi to hand feeding (e.g. by giving them treats) get very close to their koi and recognise diseases very quickly. If necessary, the affected koi can simply be fished out and treated separately. Good, over-the-counter medicines are available to koi enthusiasts in specialist shops. The most important measures for disease prevention are top quality food which is used up in a maximum of three months after opening so that the vitamins do not have a chance to decay, the right amount of fish to match the water volume, good water quality, regular partial water changes and a stable pH value.

Successful koi keeping is not rocket science! But unlike a small biotope pond, the right size and a few technical investments are needed, regular control of the water parameters is highly recommended and the right diet is a guarantee for long term healthy fish.

© 05.02.2022
Heiko Blessin
Heiko Blessin
Dipl.-Biologe

Tauchen, Fotografie, Aquaristik, Haie, Motorrad

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