Koi Fish Care in Aquarium – Is It Possible?

Koi Fish Care in Aquarium – So much articles write about colored Japanese koi fish. So many sites and specialized literature discuss about them that at first glance it seems that nothing has been added. However, one aspect, namely the keeping of these fish in the aquarium, is very little covered.

Koi fish is traditionally a pond fish. In any pictures featuring these fish, koi appear always top-view. I would call this a stereotype, which becomes easier to destroy the more the aquarium technique improves.

koi fish care in aquarium

In fact, the original koi were specifically bred for observation from above, but many modern breeds appear to do better in an aquarium. How do you get the most out of keeping koi fish in an aquarium with a minimum of frustration? This is exactly what will be discussed in this article. I hope it will be useful to aqua designers who are concerned with finding new forms of creative implementation and will be of interest to all other aquarists.

Keeping Koi Fish In An Aquarium

Koi fish is a strong fish and you can keep it in an aquarium in any way, but for complete success, it is important to go beyond the amateur notion of a home pond. In the average home aquarium mixed with barbs, catfish or goldfish in getting involved with young koi fish, angular, not yet “mature”. In general, I paid little attention to them until I saw for the first time huge, purebred ten-year-old fish in a pet shop.

You can limit yourself to keeping small individuals in a relatively small four-hundred-liters aquarium, but then you will never see all the beauty of these amazing fish. And I see no sense, from an aesthetic point of view, in getting involved with young koi fish, angular, not yet “mature”. In general, I paid little attention to them until I saw for the first time huge, purebred ten-year-old fish in a pet shop.

Koi Fish Care in Aquarium – Equipment and Accessories

Koi fishes have no particular complaints about the quality of the water but it would be wrong to start such fish and completely spoil the perception, not providing better transparency of the water. We cannot talk about long-term biological balance without external interference, and we cannot dispense with good equipment.


Filtering must be powerful for koi fish care in aquarium. An external filter (or even better, two or even three) of large capacity and with a good filter capacity. A couple of Fluval FX-5 (as the minimum required) and a weekly change of one-third of the water with fresh water do the job. It is not worth rinsing the filters according to any specific schedule. In order not to once again wash off the beneficial microflora from the substrate, this must be done as the filters become dirty, finding the right time to reduce the water pressure at the outlet.

An important condition for filtering materials is that they should not be too finely porous and finely grained, as they will quickly clog. When selecting a filter, I would not forget to pay attention to Eheim as well, including models 2250, 2260 and 2080. The last model is good because it has two intake pipes, which improves the efficiency of collecting dirt.


This is the best variant. But I am not a supporter of ducts in an apartment (especially in someone else’s), therefore, no matter how tempting it sounds, such an idea needs to be weighed a hundred times before it is put into practice. Although if there are prerequisites to approach the issue on a grand scale, then you can not get involved with the water supply system and the dangers associated with it, but organize a convenient storage tank for several hundred liters.

UV sterilizer

A UV sterilizer is a very useful and welcome device for a koi fish care in Aquarium. Of those that I have used in my practice, I can recommend Tetra or JBL. But it’s better not to mess with Aqua Medic. With all the advancement of the water passage system declared by the manufacturer through the body, the pipes of the latter are made of too thin and fragile plastic. The slightest extra effort during tightening will lead to breakage. I don’t even want to talk about the Chinese. Depressurization of the case is common here.

If you go along the path of saving, then it is quite possible to use pond sterilizers. They are cheaper and, in principle, fit. But it must be remembered that in pond models, the gap between the lamp and the body is larger than in aquarium models, and, accordingly, they have a lower irradiation efficiency. Powerful 11-18 watt aquarium uvishnik, in relatively small volumes is always better.


The air should be stable enough. Koi fish easily tolerate a lack of oxygen in the water, and even a complete lack of aeration, provided there is good filtration, is unlikely to lead to the death of fish. The question is, how long can you keep your peace of mind while listening to the squelch of koi fishes swallowing air near the surface of the water. Another extreme is asphyxiation caused by excessive oxygen dissolved in water. But this rather concerns carp wintering in ponds with excessive aeration.


Heater for obvious reasons, there is no need to use. There is also no need to cool the aquarium. Despite a reputation for being cold-water fish that often live outdoors all year round, koi fishes adapt easily to summer temperatures. In an unusually hot summer of 2010, my sponsored koi fishes endured more than 30 ° C water without any significant changes in behavior.

With an increase in temperature, it is more correct to talk about a significant increase in general metabolic processes and, as a result, more rapid pollution of the aquarium. But when it is really important to take into account the temperature moment, it is when transplanting street koi fish into an aquarium in the cold season. This should be done delicately, gradually equalizing the temperature for at least an hour. Also, you need to be prepared that koi fish transplanted from the cold can produce a lot of mucus and the filter can get clogged after hours.


There should be a lot of light. It is important. The better the aquarium is lit, the more contrasting and brighter the koi fishes will look in it. The range of lamps used is a matter of personal preference. I love the cool tones that give the water contrast and clarity when combined with Sylvania Gro-lux dye lamps. The best option would be to use good metal halide fixtures.

Koi Fish Care In Aquarium Example

keeping koi fish in aquarium

Adaptation in the aquarium.

At first, koi fishes  planted from a pond into an aquarium can behave cautiously:  get scared when approaching the aquarium, hide in corners, etc. Gradually, usually from several weeks to several months, koi fishes are mastered. The younger the fish, the faster the adaptation will be. You can speed up the process by adding goldfish to them, for example comets. This does not matter, and they will have fun scurrying around the aquarium, carrying koi fish along with them. Later, when everything is working out, the goldfish can be removed.

keep koi fish in aquarium


Important criteria for the choice of feed should be the maximum preservation of water quality, as well as the presence of color enhancing components. The main source of food for koi fish in the aquarium is properly selected dry pelleted food, which contains spirulina, axtaxanthin and / or other carotenoids. However, the koi diet can be supplemented with fruits and vegetables, which must be cut into pieces for ease of consumption. All food debris should be removed from the aquarium as soon as possible. And do not forget that it is better to feed these fish several times a day in small portions. For this purpose, it is very convenient to use an auto feeder. The daily feed rate dispensed at one time can easily cause an instant flash of ammonia, and the same amount, when divided into 2-3 portions, will be recycled by the filter.

Aquarium Decoration

In short, this is the case when the fish itself is the main focus of the aquarium, and maybe the entire room. Therefore, already at the stage of choosing a breed, you need to look at the interior in which the aquarium will be located. It will not be possible to advise unequivocally, that for example, a dark background and soil are needed under red koi fishes, and under a light gray or beige background it is better to take white fish with red spots. For each specific case, its own, special option will be optimal. One thing can be said for sure: for aesthetic and hygienic reasons, the number of decorative elements should be minimal.

Koi fishes will be really happy if they use sand as soil, but then its layer should be such that the bottom is not exposed. All important communications running along the bottom: hoses, wires, sprayers, etc. need to be laid with stones, and it is better if you first grab them to the bottom with silicone. You don’t have to worry about the stagnation of the fine-grained soil. The ventilation will still be the same. All soil will be repeatedly probed, dug up and transferred from place to place. You can also use not too sharp gravel or pebbles. Here it is for your taste. But for me personally, most often I like fine, light sand.

koi fish in aquarium decoration

In this article, I deliberately omit another aspect of keeping koi fish in an aquarium, namely winter overexposure. In this case, slightly different techniques are used than when kept in a decorative container.

Bottom Line

In conclusion, I want to draw the attention of aquarists to the most common koi fishes and so-called leather or naked koi fishes, which can be used for decorative purposes. Today there are about 50 species of koi fish, so there is plenty to choose from. Some of them look very decent in an aquarium. And with the right approach, believe me – they will look no worse.

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