Answer: 25 inches of koi per 10 square feet
Explanation: I've always used the 10 inches of fish to every 100 gallons method - so that means roughly 10, 10-inch fish for a 1,000-gallon pond.
A ten square pond at 3 ft deep is roughly 234 gallons so using this method, you would be good at around 23-25 inches of koi