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Koi fish: the king of ponds

Koi fish are a group of fish that originated from the domesticated common carp (Cyprinus carpio). Common carp were known for their various colors many centuries ago in their natural habitat in Asia, especially China. They were later selectively bred for their color in Japan, hence the name koi fish (Japanese koi fish), as they are known today.

There are many different varieties of koi fish that vary in color, size, pattern, and type of scales. Simply put, koi fish are some of the most beautiful pond fish available. They have become so popular in the last century that they can now be found in ponds all over the world.

Those who keep koi fish know how delicate and important it is to maintain their living environment. As with all fish, a hobbyist must understand all of the basic needs and requirements of koi fish.

Here are some great general tips on how to make koi fish thrive in your pond.

Pair of kois

Description – Appearance – Morphology

The number of rings around the Koi’s outer scales suggests its age, where a ring forms every two years.

Aquarium Maintenance and Conditions

Although it is not very difficult to care for koi fish, it can be very challenging if you cannot maintain it well. They may look elegant, beautiful, colorful, but they are very messy in nature as they produce a lot of waste that can easily cloud the pond water. Therefore, you must keep the water clean frequently, well balanced with oxygen and other elements, so that they can survive in each season.

If you have a proper and well-constructed Koi pond, it will not be too difficult to maintain it for a few minutes every couple of weeks. By cleaning the Koi fish pond regularly and regulating the water temperature, your fish will be able to live happily in the pond.

Group of kois eating

Pond Size

Koi fish can grow very, very large. The size to which they can grow is determined by several factors, especially the environment in which they live. If their habitat is well maintained, koi can grow quite large and also much healthier, living 25-30 years. Exceptional koi can live for over 100 years and the foundation on which everything else is built is a properly sized pond.

The ideal size of pond to keep koi should contain at least 925 gallons of water. The most important thing when planning the size of your pond is the depth of the water in it. Koi should be kept in water that is at least 3 feet deep to help them find cooler water in the summer and warmer water when it is cold. 925 gallons of water should provide enough space for five koi fish, if all the water parameters are correct.

One of the most important things to keep in mind is that the bottom of your pond should not be covered with hard gravel or rocks. Most koi keepers use a completely smooth bottom or fine gravel. This is handy because koi spend most of their time at the bottom of the pond when it’s cold.

The deeper they rest during the winter months, the warmer the water is for them, and when they stay deep, they often come into contact with the bottom surface. If the surface is too hard, their soft bellies can be injured, which can lead to serious infection or even death.


Proper water filtration is very important to the well-being of your koi. Unsanitary water conditions are considered the number one reason for the death of these fish. Quite simply, water quality is the most important factor when keeping all species of fish.

Always make sure that the water is properly filtered, well oxygenated and that all waste is removed from the environment. Keep in mind the exact needs of your fish at all times, as they can change due to the number of fish, maturity and temperature. Expert aquarists advise koi keepers to use high-volume filters to save time and effort. Ideally, your pond should have a bottom drain for easy cleaning and water changes.

Water Parameters

Koi fish are hardy species, so they are very easy to care for. But they can acquire various health deformities if the water conditions are not well maintained. Therefore, as a Koi owner, you must maintain certain water quality, such as pH fluctuation caused by acid rain or low potassium hydride, high ammonia and nitrite due to excessive fish waste, overcrowding, etc.

You have to maintain decent water parameters to keep your Koi healthy. Keep the ammonia level at zero, the pH level should be between 7 and 8.5, and the minimum amount of oxygen should be around 6 mg/litre. Make sure there is no iron, chlorine, lead, zinc or copper in the pond.

Additionally, you can keep your pond water high in minerals, which will help prevent the toxic substance from dissolving into its habitat. Meeting all of these requirements will ensure you have a decent water environment for your koi pond.

Koi fish are known for their ability to survive in a wide range of water temperatures. They are moderately cold hardy, as they can survive the usual temperatures of most climates. However, like most species, they cannot tolerate sudden changes in temperature.

Since they are cold water fish, they prefer the water temperature to be around 59 to 77 Fº. Therefore, the metabolism of koi fish is greatly influenced by the temperature of the water in which they live.

In cold climates, they should generally be able to survive easily as long as the depths of the pond do not freeze. Large portions of the water surface must also be open for gas exchange within the pond. During the summer, consider providing a shade for the pond if it is not deep enough so that your koi are not exposed to direct sunlight.

Kois underwater


Keeping the water in good condition is particularly important when it comes to keeping koi. They need excellent conditions to thrive and reach their full potential. One of the most important things when keeping koi is making sure they have enough oxygen at all times.

The dissolved oxygen level of the pond should not drop below 4-5 milligrams per litre. On the other hand, if the dissolved oxygen level drops below 2 milligrams, it can be detrimental to the koi. Therefore, make sure that the level of dissolved oxygen should be between 7 and 9 milligrams per liter of water.

Installing a waterfall or fountain is a great idea to supply oxygen and also make your pond even more alive and beautiful. During the summer, koi fish eat much more and the oxygen levels required are much higher. Keep this in mind when transitioning from one season to another. Possible Diseases

Poor water quality, crowding, and other environmental factors can make koi sick. When a koi fish is affected by parasites or a bacterial infection, it will display some sure signs of its illness.

If the fish is not eating, it lies listlessly near the surface of the water, panting or moving away from others; or has ulcers, broken fins, cottony tufts, etc., are symptoms of diseases.

The ideal level of ammonia in the pond should remain around 0.00 pm. But if the ammonia level reaches a certain degree, the koi fish will show excessive secretion of mucus and slime. Additionally, there will be red burn marks on their fins and gills.

They will become sluggish due to lack of energy and will have less physical activity. Koi owners should introduce beneficial bacteria to the pond to mitigate the risk of ammonia buildup. But the main precaution should be to partially change the water to improve the health of the fish.

You should not place nets around the koi fish pond as it can stress them out and suppress their immune system. Also, it would make them more vulnerable to microbial infections.

Diet and Food

Koi are kept for their bright color and the way they play. Their pigment and overall health are greatly affected by the way they eat. Feeding them properly will give you great results, but the most important factors to consider when feeding koi is the type and amount of food you give them.

There are many potential food sources for koi. With that in mind, you should provide them with a varied diet of different types of food. They are usually fed with pellets and floating sticks; however, they also like live foods, such as bloodworms and river shrimp.

One thing you shouldn’t do is overfeed your koi. There are several negative effects caused by overfeeding, such as polluted water from overweight fish as food debris disintegrates at the bottom of the pond. With this in mind, you should only feed your koi fish food that they can eat in five minutes. If there is anything left uneaten after feeding, be sure to give less food next time. The food needed for your koi varies greatly depending on the temperature of the water; they eat much more if the water temperature is higher, and vice versa.

You should feed them two or three times a day for 5 minutes per session. If the water is cold, approximately below 69.8 degrees F, they should be fed only once a day. If the water temperature is below 55.4 degrees F, their digestive system shuts down, so you shouldn’t feed them at all.

Also, in warm water conditions, around 7.2-82.4 degrees, Koi are very active, so you must be careful not to overfeed them.

Koi fish can lay thousands of eggs in a season.


Koi fish can lay thousands of eggs in a season. While some hatch, most do not survive, and some are eaten by other koi or other large fish. After the eggs are fertilized, the hatchlings swim to the bottom of the pond to cover themselves with pond plants until they are able to swim and are ready to feed.

Behavior and compatibility

Koi are nervous fish but, in general, they are very friendly species and do not argue with their other fish unless their natural living conditions are not disturbed. Once they get comfortable with you and recognize you, they will love to be fed. However, when under stress, they may skip feeding and hide at the bottom of the pond. Females are more social than males. Goldfish, grass carp, or plecos can be ideal tank mates for koi. This is because they all share the same living conditions to survive.

Are Koi Fish Right For Me?

Koi fish are a highly desirable species to keep in ponds as they require little maintenance. When it comes to caring for koi fish, they can do it themselves for the most part. But it is up to the aquarist to take care of the pond and keep it clean and provide it with the proper food that it requires for the koi to thrive.

How much cleaning you need to do depends on how good your water filtration system is. If you have an efficient system it will require minimal maintenance in contrast to a poorly built pond system which will force you to do a lot of work to keep the Koi comfortably.

In addition, you have to feed them at least twice a day, but it is not good to overfeed them, which can reduce the quality of the water and their obesity problems. They have various feeding requirements for each season. If you are willing to fulfill all these responsibilities to keep them healthy, continue with the process of learning how to take care of them and get them.

How many Koi can I put in a 1,450 gallon pond?

If you are a beginner, you should not overcrowd your pond with other fish if you have koi fish. Although koi are peace-loving animals, they do not usually like to have other families of fish in their territory. But when it comes to their own family, although they are very social with their kind, you need to know a few specifics to determine how many koi you should keep.

Each pond must keep an adequate number of Koi fish. The perfect parameter in a well-constructed 1,450-gallon pond with a depth of 90 to 120 centimeters. Such a pond could easily house up to 30 koi fish about 15 centimeters long sustainably.

Do Koi Ponds Need Sun or Shade?

Koi fish specifically prefer a pond that has a certain temperature range. However, if the pond water is too hot, it will cause unnecessary stress to the fish. To create an ideal climate for your koi fish, choose a pond that is situated in an area that is partially shaded during the day, receiving a few hours of shade each day.

Can koi fish bite you?

No, koi fish cannot bite you as their teeth are deep in their throats. However, they can mistake your fingers for food and suck on them.

Do koi fish need light at night?

No, you do not need to keep the light on at night for koi as it does not affect their sleeping habits. However, you can use artificial lighting to see the depths of your pond.

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