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Can You Keep a Koi Fish in an Indoor Tank? Aquatic Facts & FAQs

Rachael Gerkensmeyer

By Rachael Gerkensmeyer


gold koi in aquarium

Koi fish can be found living in ponds around the world, whether for farming or aesthetic reasons. However, not all climates are conducive to outdoor pond living, and not all people who would like to keep Koi fish as pets have the space outside for them. So, can a Koi fish be kept in an indoor tank? Yes, they can! Read on to learn more.

Koi Can Do Well in an Indoor Aquarium

While pond living is ideal for Koi, these fish can do well in an indoor aquarium as long as they are not overcrowded in their environment. Granted, you can’t keep as many fish inside as you could in a pond outdoors—unless you live in a huge mansion where an indoor pond can be constructed. If you’re like most people, though, you likely have room for an aquarium but not an actual pond. Maintaining a Koi aquarium is much different than managing an outdoor pond, but the process for caring for the Koi is the same as for any other kind of fish in an aquarium.

Here’s What Size Aquarium a Koi Fish Can Live In

To determine what size aquarium you need, you have to decide how many Koi fish you want to keep in your home. A company called NEXYDAYKOI, which sells Koi fish to customers in many locations throughout the United States, recommends that a 12-inch fish be housed in a 100-gallon aquarium.1 So, if you want to keep two 12-inch fish in one environment, you will need a 200-gallon aquarium. According to Kodama Koi Farm,2 you can keep smaller Koi in smaller tanks:

Size of Aquarium Number of 4–6-Inch Koi Number of 6–8-Inch Koi
15 to 20 Gallons 6 3
40 Gallons 15 7

It is important to ensure that you do not overcrowd your aquarium, as it could affect the health and size of your Koi. It also makes for more management work than should be necessary. It’s better to be safe than sorry and to ensure that your Koi fish have plenty of room to swim, explore, and thrive.

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Aquarium Setup Recommendations

gold koi fish in the pond
Image Credit by: noypb, Shutterstock

The first thing to do when bringing one or more Koi fish home is to make sure you have all the necessary supplies to set up your aquarium. Everything must be in place and the water conditioned before your fish can be put inside. Here is what you will need in addition to a properly sized tank:

  • Aeration system
  • Water filter
  • Thermometer
  • Heater
  • Cleaning kit
  • Aquarium light

Setting Up Your Aquarium

The first step here is to find a good location for your new aquarium. Keep in mind that it will be extremely heavy once it’s filled up with water and fish. Place the tank on a shelf or table that is solid and sturdy, or put it on the floor if you aren’t sure that any elevated surfaces will hold it. Once your aquarium is in place, rinse the filter, install it, and then fill the tank with water. If you use tap water, it’s important to add a de-chlorinator and conditioner product, as chlorination is harmful to Koi.

Next, turn on the filter and install the thermometer. The water should be between 68 and 77 degrees Fahrenheit. If necessary, set up the heater and get it running to achieve the proper temperature. Then, fill your aquarium with the plants and other attractions and/or objects that you have chosen to create a nice environment for your fish. Finally, you can acclimate your Koi to the aquarium.

Acclimating Your Koi to their New Aquarium

Koi fish in an aquarium
Image Credit by: AAFFaaff8, Shutterstock

Once you are sure your Koi aquarium’s water is between 68 and 77 degrees Fahrenheit, place the bag that your fish is occupying in the tank without opening it. Let the bag hang out for about half an hour so the water inside the bag reaches the same temperature as the aquarium water. After 30 minutes or so, you can open the bag and let the fish out into the aquarium. From there, your Koi can explore their new home before having their first meal.

The Benefits of Keeping Koi Fish Indoors

There are a few benefits of keeping Koi fish indoors as opposed to outside, though it’s important to remember that there are just as many advantages to keeping Koi fish in a pond outdoors.

  • Enjoy the Sight of Your Fish Anytime

When keeping Koi fish indoors, you can enjoy looking at them at any time of the day or night, no matter what season it is. There is no need to bundle up in warm clothes just so you can go out and see your Koi during the winter. You can simply check out your fish from the comfort of your couch.

  • Caring for Indoor Koi Is Easier

Taking care of a small aquarium and the Koi living inside of it is easier than managing a large pond on your property that is always being assaulted by the outdoor elements. You will spend less time cleaning your aquarium than you would a pond, and you can more easily spot when there’s a problem.

  • It’s Fun to Feed Koi in an Aquarium

Koi fish are typically friendly and smart, and they enjoy eating from a human’s hand. Once your Koi learns to do so, everyone will enjoy watching their movements when they swim up to your hand to take food from it. They might even jump out of the water a little!

In Conclusion

Koi fish are lovely animals that deserve all the attention that they get. They thrive in outdoor environments, but they can have happy lives indoors too. You’ll need to make sure that your Koi has plenty of space to live in and that their aquariums are properly set up and managed. That said, these responsibilities are less strenuous than if you were to keep Koi fish in a pond outside.

Featured Image Credit: Huy Thoai, Shutterstock

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