How many Koi fish can you keep in 85 gallon tank?

Answer 1

Koi are a type of carp and can get very large. 135 gallons is not enough room for Koi to be kept for a long period of time. They should be kept outdoors in over 500 gallons, constituting a pond. Only fry can be kept in an indoor aquarium but then they will have trouble adapting to an outdoor environment.

Answer 2

When it comes to Koi, you need to stock based on the average adult size even when they are still babies. The best way to do this is to take the number of gallons for your tank (or indoor pond) and divide by 100, that would give you the number of Koi.

For your 85 gallon, you will not get a whole number when you do the math, which means that you should not keep any Koi in the tank; if it was 100 gallons, then you could manage with 1.

While this may seem excessive, it really isn't considering the size of an adult Koi, and the waste they can produce.

You would be better off looking at fancy goldfish such as fantails as you could have 5 in your 85 gallon provided you have excellent filtration, and perform weekly maintenance which includes changing at least 50% of the water.