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

Keeping Koi in an 85-gallon tank is not recommended, as they require significantly larger space to thrive and maintain good water quality. Koi fish can grow quite large, and keeping them in a tank that is too small can lead to overcrowding, stress, and health issues. Ideally, Koi fish should be kept in outdoor ponds that provide them with ample swimming space, proper filtration, and stable water conditions.