Many people mistakenly think they need a big yard and big pond to enjoy Koi, but that is not true.

We can keep and enjoy Koi with any space even in an indoor aquarium. In Japan, the JNPA (Japan Nishikigoi Promotion Association) promotes keeping Koi in an aquarium. So you no longer have to give up enjoying Koi because you live in an apartment or because you lack backyard space to build a pond. Learn our best tips for aquarium koi keeping success!


In this article we cover the following on koi fish in aquariums:

5 Benefits of Raising Koi in Aquarium Tank

You may assume that koi are meant for backyard ponds, but in fact there are several advantages to why you may choose to set up an aquarium indoors vs. in the backyard. For those who live in apartments, this might be your only option to raise our koi fish for sale. Study our tips and enjoy the hobby!

Contact us or comment below with your experiences and any questions we have not yet answered.


1. Koi are easy to keep, and an aquarium takes up little space.

Koi adapt to their environment and grow according to their space. So they will not outgrow the aquarium nor jump out. Koi are also strong. Unless there is a drastic change of environment, Koi can live in water temperatures of 40–95 F°. They also can easily survive for a week without food (if you have to go on vacation, for example).

2. You can enjoy Koi every day regardless of the season.

Koi are cold blooded fish. So when winter comes, outdoor Koi go dormant; but because water temperatures indoors are stable, indoor Koi stay active. You can feed them every day and be with them every day throughout the year.

3. Koi are friendly and can eat from your hands.

Koi are known as friendly fish. Once they get comfortable with their new home, they could eat food from your hands. They can be your perfect indoor companion.

4. A Koi aquarium is a perfect room feature.

Koi are known as living jewels; and with over 100 different varieties of koi, none are exactly the same. An aquarium of colorful Koi will be an eye-catching focal point for any room.

5. Koi fish aquariums relieve stress.

It is also known as aquarium therapy. Aquariums are known to lower a person’s blood pressure and heart rate.

What You Need to Start a Koi Fish Aquarium

The following items will help you on your way to setting up an aquarium. None of this is specific for koi and the main adaptation to fish keeping is the amount of koi you keep in the tank. These are common items to use for your aquarium management.

  • Aquarium – Koi will grow according to the size of the aquarium. Pick the aquarium for the size of Koi and the location
  • Cover – An aquarium cover prevents Koi from jumping out and also prevents evaporation
  • Aquarium stand – An aquarium filled with water is heavy; so ensure your aquarium stand can support it
  • Filter – Koi eat their food and pass waste in the aquarium. A filter is critical to maintain a healthy environment for Koi. It reduces the number of water changes and the stress on Koi
  • Aeration system – It supplies air bubbles to the aquarium. Koi need oxygen to live just like we do
  • ThermometerSetting a comfortable water temperature is critical to maintain Koi health. Around 75 F° is comfortable for them. Koi do not like cold water or drastic changes of temperature between the seasons. It is best to keep water temperature above 70 F°
  • Heater – Useful to maintain comfortable water temperature
  • Cleaning kit – Bottom cleaner, net, algae scrapers help keep the aquarium clean
  • Aquarium light – It is not a necessity, but makes the aquarium look more attractive

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How Many Koi Can Be Kept In An Aquarium?

There is no specific number of Koi for aquarium; but here’s a general rule of thumb for your reference:

Aquarium Size Number of Koi (4-6 in. long) Number of Koi (6-8 in. long)
15–20 gal. 6 3
40 gal. 15 7


DO NOT overcrowd your koi in the aquarium. The more koi, the more cleaning and potential for your system to have deficiencies.

Preparing Aquarium for First Time You Receive Koi

IMPORTANT – Ensure these three things are taken care of when bringing in new Koi:

1. Finding a location

  • An aquarium with water IS heavy. Please make sure you have a solid flat place to support the aquarium
  • Avoid a location with direct sunlight. It raises the water temperature which could cause algae blooms and decrease oxygen levels
  • Avoid a place where your family is always walking around or making noise. It causes stress on Koi
  • Ideally select a location with easy access to water because aquarium maintenance requires regular water changes

2. Preparing the aquarium water

  1. First rinse the aquarium and filter lightly
  2. Fill the aquarium with water. Note: Tap water contains chlorine; so please add dechlorinator if you use tap water
  3. Turn on the filter

3. Acclimating the Koi

  • Acclimate the Koi to the aquarium’s water temperature by floating a bag of Koi in the aquarium for 15–30 min.
  • Keep water temperature around 68–77° F

How to Maintain a Healthy Koi Aquarium

In a nutshell, avoid overfeeding, overcrowding, and cleaning or changing water too often.

Feeding Guidelines

It is important to feed properly. We recommend you also read our guide on how to feed koi.

Here’s how often to feed koi in aquarium:

  • Feed once a day, just enough for your Koi to finish the food in 5 min
  • Scoop out any leftover food
  • Overfeeding Koi will make them produce more waste which ruins water quality and could make your Koi sick.

Water Maintenance Guidelines

Clean the aquarium once every 2–4 weeks. There is no need to take your Koi out.

Here’s how to do your water cleaning:

  1. Prepare water in a bucket a day before, or add dechlorinator to the bucket’s water before use (with dechlorinator you do not need to wait one day). 
  2. Use bottom cleaner to clean and discharge 1/3 of the aquarium’s water
  3. Use net to take out any large debris
  4. Rinse filter lightly. Do not clean the filter too much. It removes beneficial bacteria
  5. Add water from the bucket
  6. Add beneficial bacteria product like Niigata Water Bio to keep water healthy

Aquarium Koi Photo Gallery

Buy and Start Your Koi Fish Aquarium

Small, young Koi are great for starting your Koi aquarium, because their smaller size is easier to manage for aquarium’s limited space. Send us a koi request for the type of koi you are looking for and we’ll find the right size to fit your aquarium.