An acrylic acid resin or glass aquarium of 60 to 90 cm long is the handiest size to keep koi in.
In the case of 60-cm-long aquarium, 5 to 6 koi of around 10 cm long is the best. The case of 90-cm aquarium, the maximum number of koi should be 20. The most important aspect of taking care of koi is the water quality. To maintain an adequate water quality you should also check the smell of water. If it smells bad, change about 1/3 of the total water volume at a time. If you use tap water, don't forget to add a counteragent to treat the chloride.
A set of aquarium, filtration equipment, aeration pump, cover of the aquarium, thermometer, pebbles, and occasionally heater are musts for keeping koi in a small aquarium.
Prior to releasing koi into an aquarium, you must adjust the temperature by placing a plastic bag containing the koi into the new water for about 30 minutes. Don't forget to cover the aquarium after releasing the koi into it.
Feed your koi 2 or 3 times a day. The amount of food that the koi can finish eating in a few minutes is the best amount.
Change about 1/3 of the total water once every 2 or 3 weeks and clean the filtration system once a month. Decorating your aquarium with some ornaments on the pebbles will make it look more attractive.