If you’ve read our other article on “How Many Fish per Gallon,” you know it’s not an easy question to answer, especially for a mixed species tank. However, for koi per gallon, there is a much simpler answer:
For each koi you have, we recommend 250 gallons at MINIMUM!
What are you talking about? That’s way too high! I’ve had one fish for 10 years in a 100 gallon pond and it’s fine!
Congratulations! You’ve likely stunted your fish. Look, I’m not trying to make money by selling you more fish than your system can hold and waiting for a few to die. I’m trying to make your life easier and your fishes’ lives healthier. Koi are carp, like their goldfish cousins, and most have the genetics for extreme growth.
I’m not saying your 6″ koi needs 250 gallons, but the 24″ behemoth it will become needs 250 gallons.
Now, it’s true, not all koi will get that big. But how do you know? You have to give them the room! Not only will it make your fish happier, it will make your filtration happier too. Ready for the worst part?
If you have reproductively-mature, breeding females, we recommend up to 500 gallons PER FISH.
Well, I heard some people hit the floor and others shouting at the top of their lungs, but hear me out. Female koi carry an egg mass that may be up to HALF of their weight. Eggs take an extreme amount of energy and oxygen to carry. If they are being chased by males, they are using more resources and energy. If you have a problem with your water quality or not enough nutrition to go around, guess who is most likely to die first?
So, to the lovely person in Southern California who just added 10 koi to a 100 gallon tank, we are so sorry someone said this was okay. We have heard so many similar stories and it is heartbreaking. You are bringing an animal into your home who has the potential to live 40-60 years and grow up to 24″ and more. Why are you not giving them the space they need to thrive? Plan your koi per gallon to make sure you give them the best life possible.
Remember, you may look at your tiny koi and think, ‘they’re so small. They don’t need that much room.’ But unless you have a signed contract that the fish will be moved to a more appropriate home as it gets bigger, you are putting this fish in a tough situation. Plan for the giant eventuality.