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Can Koi Be Kept in a Fishtank?

Koi fish are a widely popular ornamental fish matched in popularity only by the very koi ponds they inhabit. 

As amazing as a well-designed koi pond can be, they aren’t an option for everyone. Even those with a koi pond may be wondering if their koi fish can live in a tank during the winter months. 

Can Koi Fish Live In A Tank?

The short answer is yes, koi fish can live indoors in a fish tank or aquarium. Just as with any fish, as long as their basic needs are met they will do just fine. 

What are these basic considerations? They include things like a properly sized koi tank, temperature control, water filtration, water changes, and proper feeding. 

There are some advantages to keeping koi in a tank rather than a pond. They are very attractive and can be the focal point of any room or office. In a tank, you can enjoy them year-round regardless of the outdoor weather. 

In fact, many people with koi ponds choose to bring them indoors during the winter. This makes it easier to keep an eye on their wellbeing and they will continue to grow in the otherwise dormant winter season. 

Koi Fish Minimum Tank Size

The primary concern when deciding to place koi in a fish tank rather than a koi pond is space. One of the main accolades of the koi fish is its large size. This must be taken into consideration when selecting a fish tank. 

A well-cared-for koi fish can reach sizes of 24 inches in length with the largest reaching a massive 36 inches long! Even average domestic koi can reach sizes of over 1 foot long. This is much longer than the vast majority of home aquarium fish. 

The growth of koi and most other fish is self-limited to the size of their aquarium habitat. While this may be true we don’t want to stunt their growth potential by putting them in a tank that is far too small. 

So how large does an indoor koi tank need to be then? There are a wide variety of opinions on tank sizes. The conservative rule of thumb is 10 gallons for every inch of fish. This means a single 12-inch koi would need 120 gallons! As you can see you will need a very large tank for just a few full-size koi.  This formula doesn’t even take into consideration the large girth of koi fish.

Recommended Koi Tank Size
Koi SizeTank Size
Small Koi 2″ – 8″50 – 100 gallons
Medium Koi 8″ – 14″100 – 200 gallons
Large Koi 14″ – 24″200 – 500 gallons
Jumbo Koi 24″ – 36″500 – 900 gallons

Some people have successfully kept many more koi than this, however. Just keep in mind that you will need very good filtration and frequent water changes. You will likely also stunt the growth of your koi. 

With all of that said, you need to have a plan for if/when they outgrow their tank. Local koi clubs are a good option to rehome your koi if a pond isn’t an option at this point. 

Koi Tank Setup 

As with any aquarium, you will want to make sure you have the following:

  • Fish Tank – The bigger the better for your koi
  • Aquarium Stand –  Make sure this is designed to hold the weight of your tank
  • Tank Cover – Koi are known to jump on occasions
  • Filter – Koi fish are dirty. It is very important to get a large filter that can cycle the entire volume of water at least 4 times an hour
  • Heater – Koi can survive a wide temperature range but 60-75°F is ideal.
  • Thermometer – Thermostats built into heaters have been known to fail. So it’s best to have a standalone thermometer to monitor temp
  • Water Quality Test Kit – This will help you monitor water quality and stay on top of water changes
  • Aeration System – Koi are large active fish and need adequate dissolved oxygen. 
  • Aquarium Lights – While not necessary they bring out the beauty of your tank!

Set the tank up in an area that makes for a good focal point but is not in a high-traffic area. It is important to place the tank where the fish don’t get frequently startled and the tank isn’t bumped or jostled. 

It’s also important to make sure the tank isn’t placed in direct sunlight or a drafty area. 

Indoor Koi Tank Care

As stated earlier, koi are large dirty fish so staying on top of your tank maintenance is key. You will want to ensure you are cleaning the aquarium once or twice a month to include a water change. 

Use a gravel vacuum to clean the gravel while draining approximately ⅓ of the tank water. Use a net to remove any large debris and clean the glass of any algae build-up.

Gently rinse the filter with water from the aquarium. Cleaning the filter this way retains the beneficial bacteria. 

Feeding Koi Fish In A Tank

Feeding koi in a fish tank is really no different than feeding them in a tank. Koi will eat and can benefit from a wide variety of food sources. Common koi foods include pellets, fresh vegetables, fruits, and even cereal.

But for most people, it is easiest to simply feed pellets designed for koi or goldfish. This will ensure that your koi will get everything they need in their diet. The best koi pellets will have the proper proportions of carbs, fats, and protein. 

Additionally, vitamins, minerals, and color enhancers are often added which greatly enhance their health and appearance. 

How often should you feed koi in a fish tank? In a koi pond, most people want to maximize the growth of their koi. This is done by feeding up to 4-5 times a day during optimal water temperatures. 

In a space-limited tank, however, I would recommend fewer feedings. Once per day is more ideal in an indoor tank. Not only does this keep them from growing too large too fast but it also cuts down on the waste in the water. 

Can Other Fish Live with Koi In a Tank?

There are some options if you would like to add some other companions to your koi tank. Keep in mind that the large koi already take up a lot of space and place a large load on the water quality. Adding more fish will increase these problems.

A few commonly recommended koi companions include:

  • Chinese Hi Fin Banded Shark
  • Trapdoor Snail
  • Goldfish
  • Golden Orfe
  • Catfish
  • Golden Tench

Final Thoughts

Although it shouldn’t be a long-term plan, koi fish can be kept in an indoor aquarium. I hope this gave you a better understanding of the difficulties of keeping such a large fish in a tank.