To determine the amount of fish to put in your pond, you have to measure the square meters of the surface.
To calculate the surface area is simply length x width = m² area, for example a pond which is 3m wide x 6m long has a surface area of 18m².
When introducing fish into a new pond you should allow a maximum 25cm of fish per square metre.
Once a pond has matured (around three years) you can gradually double the stocking level to 2 inches or 50cm, never add large quantities of new fish at the same time and allow for the size that they will eventually attain.
Please remember that these figures are based on a good healthy pond. Your water should have very low levels of ammonia with very good mechanical and bio filters and UV lights. Always double up on the suggested amount of equipment as South Africa has a higher temperature than European countries.
Some sources suggest one koi per 1000 litres others one koi per 2000 litres. I prefer the later.
I have seen ponds 15 000 litres with thirty koi in it. It is a disaster. There should be no more than seven fish in this pond The koi are 500mm plus and the pond water is wasted through the settlement chamber daily 100mm or 10% and the water is still dirty, murky and smelly. The koi are not happy. In this case it is better to sell some of even though you are attached to them.
The mistake that most first time koi enthusiasts is they buy a lot of small koi and don’t realize they grow quickly and you will be over stocked within a few months.