how big of a tank would koi need
We recommend the following GPK (gallons per Koi) rates based on their size: Small Koi (2 - 8): 100 - 150 gallons. Medium Koi(8 - 14): 250 - 300 gallons. Large Koi(14 - 24): 400 - 500 gallons. Jumbo Koi(24 - 36): 750 - 900 gallons. The GPK estimates are based on long term housing for the Koi. Indoor winter tanks can be small, but must accommodate enough room for the Koi to swim around comfortably.