As someone who has kept Koi since I was barely out of diapers, that website scares me. They have some good info, which is fairly factual, but the site also has very contradicting info. For example, it recommends you start with a 500-2000 gallon pond, but then recommends “about 20 Koi for a 2000 gallon pond”. If you do the math, that is like 100 gallons per fish, and that’s assuming you have a full 2000 gallons of water in the pond. Would you put a 2-3 ft. Koi in a 100-gallon aquarium?
But as I said, the site mentioned also gives some really good info. My statement saying, “Koi can get 2 ft long” was a meager one… Koi (as that website said) can and do get 3 ft long. In the wild, they have surpassed 3 ft, the record being near 6 ft long. Anyone who has properly kept these fish will tell you I was going easy on you all when I said they reach 2 ft. The very same website also recommends a minimum of a 4’ depth, which is also a wise statement. Koi can and do jump, splash, dash, etc.
Many experienced ponders will tell you they do not recommend Koi for any pond under 1000 gallons. This is because of their size, and because of how much waste they produce. Also, assuming you want more than one Koi, you would really need a good-sized pond. These fish are not for the beginner, and as someone else mentioned – perhaps some fancy goldfish would be best in this situation. Surely, you could have more than just 1 Goldfish.
I would recommend checking out links that are not trying to “sell” you any products. The first that comes to mind, obviously, is Robyn Rhudy’s aquatic website. She has kept these fish just about since the dawn of time and has a very well known website, “FishPondInfo.com”. Here is a direct link to her Koi page:
http://fishpondinfo.com/koi.htm
She also has many links towards the bottom of that page which you should feel free to read at your leisure.
I will end with a picture of an “average” sized Koi:
