Hi Ed you probably be dissapointed if you put in Koi most of us that raise Koi have pond that are measured in gallons so we can see our Koi and raise them for enjoyment. In a pond that size I doupt if you would ever see them. I currently have 9 in my greenhouse pond 1200 gallons and I am the process of digging an 8000 gallon pond beside my 1/3 acre pond in the front yard. Plan to feed water from the main pond to a 7' diameter water wheel into the Koi pond and then down a 20' stream back to the main pond. Been quite a project so far and I hope to finish by the spring. You can see some pictures of my Koi on my website.