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Can You Keep Koi In A Fish Tank? (Tips and Size Guide)

Can You Keep Koi In A Fish Tank? (Tips and Size Guide)

Koi fish have long been used to add a touch of elegance to one’s home. These huge fishes can grow up to enormous sizes, so you may have only ever seen them in a pond outside – at least, that is the ethnic, Japanese image.

However, many people are unaware that these large goldfish can actually be kept at home as well!

You most certainly can keep koi in a fish tank at home, as though they can increase a great deal in their size, it is only limited to the size of their surroundings. So if you were to keep koi at home, they will adjust to your tank’s size, though a large one is still recommended. 

These fishes are fancy, and there are other factors as well, that need to be met when keeping koi as pets. If you would like to know more, continue reading this article!

Can You Keep Koi In A Tank?

Though you will normally find koi fish in backyard ponds, it is possible to keep them in a tank. In fact, they can add a beautiful touch to your living room and may even thrive well indoors in harsh conditions.

Koi Fish

These species of fish grow up according to the kind of container they are in, so if kept in an aquarium, they will grow to fit in it. 

However, being big fish, you have to be careful and keep a closed tank, as koi like to jump and try to make an escape. The ideal temperature for the survival of koi fish is around 41-91°F, so they survive in most kinds of places.

They are also very hardy and can live to go without food for at least a week.  

Koi may also benefit from being kept in a tank. During winters, when the water gets cold, koi may not survive outside, but if kept in an aquarium, they remain active in the steady temperature of the water.

They may even live a happier life with the water being adjustable according to the weather.

These fish are also known to be quite friendly, and they can also make for very active pets for fish, considering it is possible to teach koi some tricks, like how to feed off your hand. 

More: How Much Are Koi Fish?

What Is The Best Possible Setup For A Koi Tank?

It is possible to keep koi at home, but being fancy fish, they require some altered certain conditions for their survival. In order to keep koi, the following are the most important things you need to keep in check. 

1. Setting Of The Tank

The most basic requirements for the survival of your koi in a tank are its pH levels, the perfect temperature, and a proper filter for cleansing. These fishes can survive at a pH level of 7.2 to 7.4 (alkaline), but not lower than that, as they might suffer from Acidosis.

Make sure that you let your tank filter complete one cycle during the setup. 

Letting your tank go through nitrogen filtration once will allow the healthy bacteria to grow, which is good for your koi. You also need to keep the aquarium at a temperature of 18-31°C as they need warmer conditions to thrive.

An underwater heater is better as it can transmit heat evenly throughout the tank.

You can also install a light for your aquarium as these fish require around 10-12 hours of light every day. Make sure that these conditions are met at all times. Keep an eye on your fish as well, as anytime you notice discomfort, you might want to adjust the settings for them. 

2. Interesting Environment 

Tanks have many modern, adjustable benefits, but being creatures of the wild, compared to a pond, koi would most likely feel bored in a tank.

As mentioned earlier, they also like to try to escape from their aquariums, which happens due to boredom, and sometimes out of uncomfortable water conditions. 

Koi are very energetic fish by nature, so to avoid any accidents, make sure that you get a tank with a lid for avoiding any accidents.

However, to fix the direct root of the problem, you have to make sure that there is enough stimulation for your pet in its surroundings or aquarium accessories. 

These fishes really enjoy playing with aquarium pebbles and substrate. They enjoy sorting rocks and looking for leftover food between the gaps, so having the substrate full of aquarium plants, pebbles and grains will give them enough to do. Just around 2 inches of rocks would do, as more would be space-consuming. 

You can also add other sculptures, corals, and other decorations that add to the aesthetic scene of the aquarium. A shady sculpture would also be a nice addition as koi like to hide and sometimes move around these tiny objects as well. 


3. Maintain Natural Surroundings

Being natural creatures of the outdoors, it is important that your koi get enough sunlight and oxygen as much as the living conditions they require.

Keep your tank in a space in your house that gets enough sunlight and air. Keeping a tank in the cold and shade can contribute to the growth of algae in the tank from the dampness. 

Algae can stop the nitrogen cycle, which is required for the survival of koi. Make sure that your tank has enough space for the free flow of air so that it is easier for you to clean as well. 

4. Enough Space For Each Koi

Koi are big fish, and they require a lot of space to grow, so it is not ideal to pile all of them together like one normally does with other species.

Though they adjust to the size of their container, sometimes, koi fish can grow bigger than their tank. A crowded fish tank would mean a lot of ammonia and waste from the pets. 

This might make them feel uncomfortable in their living surroundings, and even cause them irritation. Additionally, lack of space can also force them to fight for room in a small tank.

For around 6 koi fish of about 4-6 inches, a tank-sized 15–20 gal shall be enough to stop overcrowding. 

As a responsible fish owner, if you are buying koi, remember to upgrade if the size of your pet increases – or else, you might be facing a number of mass deaths.

If you have a sick fish, keep them quarantined away from the others as these fish are really fragile by nature. 

More: How Long Do Koi Fish Live?

How Many Koi Fish To Keep In A Tank?

Since ponds are the ideal habitat for koi, it can be tricky to understand how many koi to keep in a tank. Being a robust species, koi have a long lifespan, can live up to 24-34 years, and even grow up to 22 to 26 inches long. Following is a table to help you get an idea of how many fish can fit in a tank. 

Size Of Fish Size Of Fish Tank Number Of Fish To Keep
4 – 6 inches  15-20 gallons 6
4 – 6 inches 40 gallons 15
6 – 8 inches 15-20 gallons 3
6 – 8 inches 40 gallons 7

This is also the standard rule-of-thumb that you can follow in order to calculate how many fish you can keep depending on the aquarium size you choose. 

How Do You Keep Koi In A Fish Tank?

Keeping koi in a fish tank can be a difficult task, and they are definitely not the species for first-time fish owners to start with. Hence, the following are a few tips you can use as a beginner koi keeper. 

1. Setting Up A Location

No matter what size your aquarium is, make sure that you keep it on a smooth surface that gets enough sunlight every day so that the growth of algae can be avoided. Make sure it is not direct sunlight, as that can alter the water’s pH and temperature levels. 

Also, keep it in a quiet place as noise can disrupt the mental peace of the koi and cause them a lot of stress. You can also keep it near a place with easy water access as aquariums require frequent water changes. 

2. Filling Up The Tank

Clean the tank thoroughly before you fill it with water. Do not add tap water, as it can be too hard for any fish to live in. If you are using normal water, make sure to filter it out, or let the aquarium filter do the job of cleansing. 

Always check the pH level and temperature of the water before you put your fish in. This is a very important step as all requirements must be met in order to help your pet koi survive. 

3. Putting In The Koi

Before you put in the koi, you should try to get them used to the water’s temperature. This can be done by first putting your fish in plastic bags and then letting them float over the water for around half an hour. Remember that the ideal temperature for koi to survive is 67–77° F.

4. Aftercare Of Tank

Maintaining the tank is also extremely important. As responsible fish owners, clean your aquarium once at least 2 weeks. This can be done without taking your fish out as well.

Simply prepare the refill in a bucket using a de-chlorinator and clean your filter by rinsing it lightly. 

This method shall be followed for a quick clean, but at least once a month, do a thorough cleaning of your tank. You can also add other additional bacteria to ensure it is enough for your koi to survive. 

How Long Do Koi Fish Live In A Tank?

Although koi grow up to be very large and can fight for dominance in a small container, they have extremely long lifespans for a fish species.

Generally, domestic koi (western variants) have a lifespan of about 15 years and Japanese koi have been known to have an average life span of about 40 years. 

Hence, koi in a fish tank with proper care and maintenance have a chance of surviving even up to 24-35 years or even more. So, if you are planning to get koi, know that you are investing in a long-term commitment. 

Koi Fish

What Size Tank Does A Koi Fish Need?

On average, there cannot be a tank too large for koi. Fish, in general, like to have a lot of space to swim around as their natural habitat is in the option.

Even if you were to get a tank-sized 1500 gallons, it would be great for your koi. In fact, if the tank is not large, you might even have difficulty with your growing koi. 

If you start out with baby koi in a small tank, you might have to increase the size of the aquarium anyway as your pet grows. Hence, getting the larger size from the very beginning is not a bad idea, except if you detest cleaning and maintenance. 

What Fish Can Live With Koi In A Tank?

All fish that require the same conditions as koi can be put into a tank with them. Ideally, medium-sized fish would be preferred, as koi can grow to be quite big, and smaller fish can get eaten by them, causing problems.

You must also make sure that you get your other fish from a reliable source so that they do not bring in disease. 

A lot of fish can grow to live with koi – grass carp, goldfish, redear sunfish, suckermouth catfish, Chinese high-fin banded shark, largemouth bass, and orfe are some species to name a few. 

How To Take Care Of Koi Fish In A Tank?

Apart from giving your koi all the basic necessities and living requirements, there are some other things you can benefit from knowing. The following are a few tips on how to take care of koi in a fish tank. 

Have Enough Room For All Your Koi

Having enough space for every koi is the most important thing to remember, as size is a very common problem faced by koi owners.

Remember that the compactness of space can stunt the growth, and in some cases, cause accidents because irritable koi like to jump out of the water. 

Maintain Clean Water

Not only do you need to maintain your aquarium’s hygiene every few weeks, you can also add extra minerals by adding granulated carbon or an under-gravel filter.

As a rule of thumb, the filter should process 350 gal. of water for every 12 inches of fish. Also, avoid overfeeding to avoid the production of extra waste. 

Since koi go around the substrate a lot, clean the gravel at least once every week. Lastly, make sure that the pH, ammonia, and temperature of your tank are always balanced. 

Aquarium Change During Winter

During winter, temperatures can drop quite a bit in the aquarium. If you notice a change in your koi’s behavior, you can shift your koi into an open tub of around 300 gallons temporarily. 

Related Questions 

What Is The Minimum Tank Size For Koi Fish?

Since koi are big fish, the minimum tank size approved for the healthy growth of your fish is at least 240 gallons. 

How Big Of A Tank Do Koi Fish Need?

Koi fish need a tank size of at least 240 gallons to grow healthily and have enough space to swim around.