It’s important to bring your ruler to the pond shop when shopping for Koi Fish. We recommend a maximum of 8″ of fish for every square yard of pond.
Every fish is different, thus we go by total inches for consistency. Let’s say your pond is one square yard, this means you should choose two fish that are both approximately 2×4″. This rule, however, is very dependent on your water filtration quality. If you happen to have superior filtration through Bio-filters, Phyto-filters, or External Filters, then you can sustain more fish. If the water is not clear or excessive algae is present it is possible that you have too many fish, thus it is a good idea to either increase filtration quality/quantity or reduce the number of fish.