For a 1,000-gallon pond, keep two to four Koi and ensure the pond is well-maintained. Koi can grow over two feet long and need a minimum of 250 gallons of water, but younger fish need less. Fish don't grow to the size of their environment; keeping fish in a small pond will stunt their growth and impact their health.

Koi need at least 250 gallons of water per fish to avoid outgrowing their pond. Putting too many small Koi in a small pond is a common mistake among owners. If the fish outgrow their pond, it's best to remove some to avoid competition for space and oxygen, which can stunt their growth and shorten their lifespans.