September 15, 2016
One Koi per 1,000 Liters (or 1 cubic meter) of Water
To maintain the quality of your pond’s water, keep in mind that fully-grown pond fishes can grow to between 30 and 50 cm in length and some of them (like Koi and Goldfish) have to be kept in shoals, so there should be some sort of “occupancy standards” for ponds.
The basic rule of thumb is to “allocate” at least 0.5 cubic meter of water for every fully-grown fish, but for Koi, the rule is at least 1.0 cubic meter for every fully-grown one of them.
These are even “modest” standards; the British even advocate 1 fish per 5 cubic meters, with large-sized filters and high temperature stability.