Hi, Dr. Bob, I have about 900 to 1000 gallon pond with 4 Koi about 6 inches long. I was thinking of adding a few more fish but don't want to upset the ecosystem as everything seems to be fine right now.

How many fish can a pond my size comfortably hold?

Your capacity will depend on the size of your fish. For fish 8 inches or less, figure 50 gallons water PER INCH OF FISH. Bigger fish require 100 gallons per inch. You can exceed this with EXCELLENT filtration.

Steve Childers fudges this by advising a minimum of 500 gallons water per fish larger than 12 inches AND EXCELLENT filtration.

I hope that helps.

Bob