Can Koi Fish Be Kept In An Aquarium?

Can koi fish be kept in an aquarium? You might be asking this question if you are not ready to invest in an indoor or outdoor pond. At the same time, you might be worried if your current koi fish in the pond will survive the hard winter months.

So, will they be happy inside an aquarium?

Koi fish can be kept in an aquarium, but it should only be temporary. Your koi fish will eventually outgrow the tank. Also, an aquarium will not be able to give the right environmental conditions as that of a pond. Keeping koi fish in an aquarium should only be on a case to case basis. 

In such a case where you really need to keep your koi fish in an aquarium, you should first know how to properly set up the tank. Even though they will stay there temporarily, of course, you should still provide them with the right tank conditions.

If you want to know when it is okay to keep your koi fish in an aquarium, keep on reading to find out more information. Further, be on the lookout for our tips and tricks on how to properly set up their aquarium.

When Can Koi Fish Be Kept In An Aquarium?

As we have mentioned earlier, you can still keep your koi fish in an aquarium, however, it is not the ideal set up. But surely, there are those instances when this cannot be avoided. Take a look at the following to see when you should go with the aquarium route.

Newly Purchased Koi Fish

Let us say you already have koi fish and they are in an indoor or outdoor pond. However, you are not interested in breeding them, so you tweak their water condition or you separate the females in order to prevent a spawn. Instead, you want to keep on purchasing new koi fish.

Is it okay to add them to the pond instantly? For some breeders, they think that it is okay to immediately add new fish to the pond as for them, koi fish thrive with other koi fish. On the other hand, some breeders opt to put the new koi fish in an aquarium first.

This is because doing a quarantine first will ensure that the new koi fish will not bring parasites or diseases to the healthy koi fish in the pond. More than that, you can also acclimatize the new koi fish with the water conditions of the pond.

In this way, once they are ready to join their new brothers and sisters, they will not be shocked or stressed too much when it comes to the new water conditions and temperature. For some, they do a quarantine of 30 days. Others are already okay with 15 days.

Koi Fry

Now this one is exciting! Imagine holding the fertilized eggs of your koi fish. It is a good idea to take out the eggs from the pond and let the fry hatch in an aquarium.

This is the best option as koi fish are cannibalistic. If you leave the fertilized eggs in the pond, the eggs might be eaten even before they hatch or the fry will not survive as they were eaten by their parents.

So it is okay to let them hatch in an aquarium. In this way, the fry will not be too stressed and their cannibalistic tendencies toward other smaller fry will be lessened as there is no competition for food.

Koi Fish That Are Sick/Injured

Of course, there will always be those times when one or more of your koi fish will go down with something or they get injured.

In the event that you really have to separate them so as not to pass on a disease or parasite to your other koi fish, you need to make use of a separate tank to contain them properly.

It will then be easier to tend to their needs and also administer the needed medication. At the same time, their distress will also be lessened as they do not have to deal with a lot of tank mates.

But once they are doing okay, you should put them back as you do not want them to completely readjust to the conditions of the pond.

Cold Or Winter Season

This is really a huge project for koi fish owners especially for those who have a natural pond set up and for those who live in a place where there are extreme winter conditions. Surely, your pond will freeze and of course, you do not want your koi fish to freeze to death.

Therefore, during the cold winter months, you really have to take your koi fish inside and let them stay in an aquarium. Of course, we are not only talking about a single aquarium here as that will also depend on how many fish you have and their respective sizes.

A lot of breeders recommend this method instead of using a heating element on the pond. Not only is it cost-efficient, but using an aquarium will also be easier to maintain.

Why Keeping Koi Fish In An Aquarium Should Be Temporary

The main reason why koi fish cannot be kept in an aquarium permanently is that they grow so rapidly. Even though you are keeping significantly smaller koi fish, they will eventually grow large.

Take for example a baby koi, he or she will outgrow the tank in just a year. So imagine housing at least five koi fish in one tank, they will surely feel that they are being deprived of swimming and resting spaces.

Unfortunately, this is the case as to why some koi fish owners eventually give their koi fish away. They get so attached to the koi fish while they are in the aquarium that they fail to prepare for an indoor and outdoor pond. By the time they grow to their full size, it is already too late.

Much more important than the size of the koi fish in the tank, it is generally unhealthy for them to be stuffed in an aquarium. They should have a large swimming space in order to swim in groups or to swim around alone.

Further, it will be easier for them to pass on diseases when they are cramped. You might also notice that they bully each other more when they are in the tank as they are constantly fighting for space.

If you truly want to grow your koi fish population, then you should consider seriously investing in an indoor or outdoor pond. In doing so, you give your koi fish the proper way of life and this will make them healthier and happier.

How To Properly Set Up The Aquarium

Now that you know the instances where keeping koi fish are acceptable, you should now gear up for the proper set up of the tank.

As we have mentioned earlier, no amount of tank set up can replicate the conditions of their pond, however, you can still ensure that at least, they get to live comfortably in their aquarium.

1. Tank Size

Make sure that you get an aquarium that is big enough to house the number of koi fish you have. Definitely, they need a tank that can carry large volumes so that they will be comfortable. The rule of thumb is there should one cubic foot with every inch of the length of your koi fish.

You can determine the tank’s cubic footage when you multiply the height, width, and length. You should also provide a cover at the top of the aquarium to minimize the evaporation of water and to make sure that your koi fish will not successfully leap out of their aquarium.

Further, make sure that you put the aquarium on top of a stand that can fully support its weight. As for the location, you can pick an area that can also provide some sort of support to the tank like a support wall or a concrete basement floor.

We show you what tank size koi fish need in detail in this article.

2. Sunlight

You should consider the amount of sunlight that will be directed to the aquarium. When there is constant direct sunlight, it will be easier to develop algae. Moreover, this will also change the water temperature.

Therefore, it is best to keep the aquarium away from sunlight. In relation to this, as koi fish are sensitive to things around them, you should place them in an area where there is not a lot of sound vibrations. In this way, they will not be too stressed.

3. Substrate

When it comes to the substrate, koi fish enjoy having rocks, gravel (big and small), and rock pieces. As they are bottom feeders, they will sift through the substrate to forage for food.

Make sure that the substrate is at least two inches deep and that there is a mixture of gravel. It does not matter whether they are natural or artificial. What matters is that there is some sort of substrate at the bottom of the tank.

4. Water Levels

For young koi fish, 29 gallons of water is acceptable. But you should always be on alert once they grow as they will need more water. Also, there should be 100 gallons of water for every koi fish that is 12 inches long.

So if you have nine koi fish that are six inches long, the 100 gallons of water will be enough for them. Following the same logic, 100 gallons of water is enough for 90 koi fish that are two inches long.

Most importantly, always pair the level of water on the number and size of your koi fish. You do not want the water to be too much or else it might end up spilling out of the tank or adding unnecessary weight to the tank.

5. Water Temperature

Koi fish are cold water pond fish, so they really do not need an aquarium heater. However, you can use that especially if you live in a place where the cold months can reach extremes.

They can withstand a temperature that is above 80 degrees Fahrenheit and below 40 degrees Fahrenheit. However, if they are in the aquarium, the temperature should be between 68-77 degrees Fahrenheit. In this way, it will be warm enough for them to have a good metabolism.

6. Proper Maintenance

As for the filtration system, it should be able to process all the water for at least three to five times in an hour. So let us say you have a 20-gallon tank, the filtration system should be able to handle at least 60 gallons of water for every hour.

You should also add beneficial bacteria in the tank in order to help in breaking down waste. Testing the ph level every day is important as koi fish prefer it to be between 7 and 9.

As for water changes, you should do them partially every week. You can take out 10 to 20 percent of the water and add dechlorinated water.

7. Enrichment

Lastly, in order to replicate what they have in their pond, you can add live plants. They will also have fun with floating live plants. However always check on them as koi fish may also eat these plants, especially in an aquarium setting where they will always swim around these plants.

How To Feed Koi Fish In An Aquarium

The way that you feed your koi fish in their pond will vary in the way that they should be fed in the aquarium. The reason for this is that uneaten food will abruptly turn into waste and it may get sucked into the filtration system.

So the solution is to just feed your koi fish enough food that they can consume in just five to seven minutes. In this way, there will not be a lot of waste and the water will not become cloudy too fast.

Make sure that you do not overfeed them as this will also pollute the water and can add too much ammonia. Another thing as to why you should only feed them enough food that will last for a couple of minutes is in the way they eat food.

Usually, they will let their food drop to the substrate and they will look around the gravel for it. Doing so highly disrupts the gravel and any loose ones will be immediately sucked by the filtration system.

So in the long run, it can clog your filters and at the same time, your koi fish were not able to eat at their heart’s content.

Giving them food in an adequate amount will let them eat the food while it is still falling inside the tank. More than that, in the event that some will be left on the substrate, it will not contribute highly to the waste in the tank.