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
- Thermometer – Setting 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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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
- First rinse the aquarium and filter lightly
- Fill the aquarium with water. Note: Tap water contains chlorine; so please add dechlorinator if you use tap water
- 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
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:
- 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).
- Use bottom cleaner to clean and discharge 1/3 of the aquarium’s water
- Use net to take out any large debris
- Rinse filter lightly. Do not clean the filter too much. It removes beneficial bacteria
- Add water from the bucket
- Add beneficial bacteria product like Niigata Water Bio to keep water healthy
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.
I’ve kept small koi in 120 gallon aquariums for years until they were ready to go out to the ponds. Currently planning a permanent koi tank in a 330, 400, or 500 gallon acrylic tank with a bead filter.
Glad you enjoy Koi even inside the house. Koi are fun to watch and raise indoors and outdoors. thank you for leaving your comments.
12′ Koi in a 230 gallon tank.
Hi Lynn
I am in Canada, fisrt year keeping pond in the pond, but pond has to be renovated . I have about the same size aquarium and I just want to be sure they are healty. I am testing water every week, nitrates are bit high so I will do a water change ( third week indoors) I think I need to cut down feeding as well. Have you ever use aquarium salt for the Koi?
i can not get my koi water clear it is cloudy for months
Do you do water change? wash filters?
Since my dad died (feb 8th, 2022), he left everything in the garage.. including fish & koi in aquarium. I don’t have any experiences but I want to keep fish. I need help and tell me what can I do for them? Do I need to buy bigger aquarium and filter.. something….
I’m not sure what my numbers / colors should read for my 5 in 1 test strips for indoor koi?
I have the strips not sure how to read them.
You never want to do a water change The same day you clean the filter. It will cause the water to get cloudy and go through the nitrogen cycle all over again cause what’s called ” cloudy tank syndrome “. Rinse the filter out a few days before or after the water change. I hole this helps. Since I’ve started doing it that way I stopped grt the cloudy tank syndrome.
I built an outdoor pond a year ago and went through the same problem. Dummy me didn’t take the time to watch and learn from U tube videos. Now I have 11 Koi and crystal clear water with a minimum of algae. It’s really quite simple. Mother Nature provides everything you need. You need to get the eco system just right. This applies to an indoor aquarium as well. You’ll need lots of wet surface for bacterial to colonize . Plants and barley straw control algae. Don’t feed more than they will eat in 5 min or so. Make a 10% Water change every week. Clean your mechanical filter without using tap water with chlorine. There are chemicals for everything you need if things go wrong however with it set up right nature will do it all. Make sure you test the water often. Some cloudiness can be removed quickly by using a flocculant . Make sure you do use the proper dosage! Too much can do more harm than good. I hope this helps. Nothing better than having clear water and beautiful healthy Koi.
I have 16 koi in a 3200 gallon “pond” I built in my yard 6 years ago.
They range from 10 in to 30 in. The only filtration I have is 50 cubic feet of lava rock with ferns planted in it installed under the eve of my house in part shade. I run a 3000 gallon per hour pump that moves the water up to the filter bed 24 hours a day. My water remains crystal clear here in Northeast Florida, and my koi are very happy campers indeed
I used algaefix, and it cleared my water in three days. Except I believe I overdosed it and it killed off most of my fish. Not saying this would happen to you but I would take fish out and keep in a different location for a couple of hours after first dose.
I want to ask why my koi fish keep dying. I want to ask Will coral stone rise the water ph. By the way I keep my koi fish in aquarium. If is about 180 liter. I use eheim 2217 classic filter.
We have a very large koi (about 22” long) in a 125-gallon aquarium tank. We’ve had him for 30 years and, because of the Osprey and eagles near us, we can’t put him out in the big pond in our neighborhood. What is the best type of food to feed him? Lately, the filters have been clogging quickly because we’ve been using food with too much fiber.
*Koi adapt to their environment and grow according to their space. So they will not outgrow the aquarium*
This is false, very disappointing to know this myth is still around. They absolutely do out grow tanks and DO NOT grow to their environment.
“Koi adapt to their environment and grow according to their space. So they will not outgrow the aquarium nor jump out.” This is quoted on this web site?
Please clarify as I would like to start keeping Koi?
the general rule for environment size is gallon=koi size. for example 5 inch koi need 5 gallon of water. if the environment has more space than needed, the koi will grow a few more inches. If the environment does not have more gallons there is no growth. For quicker assistance please email info@kodamakoifarm.com
Koi are actually a fish like goldfish that are exempt because Goldfish are one that produce growth inhibitory hormones (e.g. somatostatin) and in nature, it’s their way of reducing intraspecific competition by suppressing growth. I had koi fish 5 inches in a 75 gallon tank fit 2 years then finally got a 180 gallon for them and they have been in it 3 years with only measuring 7 inches. I put a new koi in the aquarium so we could test the theory to see if the Koi fish that were in the 75 gallon were stunted. Jack (new koi) was 3 inches and is now 7 inches (same size as previous Koi) in one year. I’m not sure if he’ll get bigger or not but the koi that were in the 75 gallon we’re definitely stunted
What type of pump and filter are the best to use in an aquarium?
Thank you for this article. Do you have a link or site where I can read about this “ JNPA (Japan Nishikigoi Promotion Association) promotes keeping Koi in an aquarium”?
Here is their website, but I am not sure if the information is available in English. https://jnpa.info/koie1700.htm
Hi….How many number of koi can I keep in my 180 gallon tank?
depending on how big the koi are. general rule is to allow the same amount of gallon space of the size of koi. example (15 inches need 15 gallons)
can I keep small butterfly koi (Petco) in a 10-gallon tank? if so, how many?
the general rule for environment size is gallo n= koi size. for example 5 inch koi need 5 gallon of water.
That is absurd and you should be ashamed for promoting it. A 15-gallon tank is only 13″ wide. A 15″ fish needs at least a hundred gallons and you know it. Your fish will die young if you try this.
I disagree with rath. I’ve enjoyed koi for many years in tanks – haven’t built my pond in my new home yet….As long as you check the parameters of your water regularly and have a large filtration system ( 500 gph for 75-100 gal tank) that’s cycled 5 inches = 5 gallons is tight but ok. Koi get lonely too. I always keep two or more together. I use salt in my tanks too-(prefer pond salt) but use cautiously. Water evaporates but salt stays (gets all over the tank cover!)
A very helpful article! I’m setting up a tank at the end of this month and housing a koi in by around August, this has come very handy.
Will you have real or fake plants with the koi in an aquarium?
How many kois could we grow in a 100 gals aquarium. Thanks
I have 6 small (2-3inches) koi in a 4ft/80gallon tank. The tank has two very big filters (Fluval FX6 and FX4), which flow just over 6000liters per hour combined, as well as a big air pump.
I change 60 liters of water a week and clean the filters once a month.
Do you think I’m over stocked with this setup and maintenance plan?
With KOI in an aquarium is it best to leave the base of the tank clear of any rocks or sand or is is best to cover the base of the tank with something.
I have a 100 gallon pond. How many koi can go into that? I saw some baby koi at a pet shop and would like to get one or two. Is that possible?
I have one 5 inch Koi that I was going to bring inside as my pond is small and will freeze so I have to empty. Will two other small goldfish be enough for companionship? Why do you suggest nothing on the base of the aquarium?
But let’s say that the water temperature falls below the freezing point. That doesn’t mean the entire pond will freeze solid. What happens first is that ice will accumulate on the surface. As the surface freezes, the layer of ice will serve as an insulator that keeps the heat in the water below from leaving the pond. This is why your pond probably won’t freeze solid, especially in Alabama. (Koi fish can’t survive a completely frozen pond, so if your pond will freeze particularly if it’s a shallow pond you should move your fish elsewhere.)
I have a 20 gallon long aquarium. I was hoping to keep 3 baby koi in it. Do I have enough room to make it permanent? If I don’t I have a pond that will be ready in a few mouths.
That may be okay. Keep in mind not to overcrowd since it is a small aquarium. You may have to clean more often as they grow.
Hi. I was wondering if I could have 3 koi in a 125 gallon tank. Would 3 be overcrowding?
Absolutely not. Those 3 koi will eventually need hundreds of gallons.
Ihave had my 2 koi and 2 shubunkin fish in a 65 gallon for about 5 months taken out of my garden pond. My shu’s are swimming around happily and eat, the koi past couple of weeks just lounge on the bottom and do not move much. They were active when I first put them in. I do bi-weekly water changes of 1/3 to 50%. If ammonia creeping up, I do more of water change. I have a Seachem Tidal 110 filter as well as a SunSun submersible filter. I feed one a day.
I have 1 Koi and keep moving up tank size. I am at 150G now and wondering if they prefer a longer tank or deeper tank? One is 4′ long and 3′ deep, The other is 6′ long 19″ deep. Thanks!
This depends on what type of environment you want to create for your koi and how the behavior is. Longer tank is good to promote your koi to be active. Deeper tank will help make the koi feed secure as they will have more hiding space from the surface.
Hi! I’m happy to have found this article! I have a 55G “standard tank” (ie. 4’x1’ for the bottom cross-section). How big can I go with the koi (ie. How many inches of fish can I support)? Also, is under gravel better or should I just use a canister filter? Thanks!
Hello, We recommend that you start with small koi such as those found in our Study Tategoi program that are 3-4 inches. Here in our office we have a few in a 40 gallon tank. Water changes and filter rinse/cleaning as appropriate. Thank you
Bonsoir , je souhaiterais savoir quelle autres espèces de poissons je pourrais mettre avec mes 2 carpes koi ?