How many Koi can I have?

This question seems common, but the answer doesn't! After several hours of searching through various websites and reading numerous articles, I've found some information that provides practical guidelines. However (and this is important!), please use this as a guideline only! I'll explain further on -

A general rule of thumb is to stock about 1" of fish for every 10 gallons of water. However, this is based on the assumption that your pond is set up to maintain healthy water quality - and healthy koi! Some of the things to consider include growth rates, waste disposal, temperature changes, and predator protection. Here's how each of these can affect your stocking rate. I should also add that opinions on stocking rates vary; this rate would mean you'd have at least 120 gallons for a 12" fish. I've read other opinions which suggest anywhere from 250-500 gallons per fish; since they are discussing koi, and since a healthy koi under good conditions can reach 3', even my guidelines recommend 360 gallons for a 36" koi.

Growth rates: Young koi can grow as much as 4-6" in the first year, and 2-4" in their second year. Therefore, if you purchase 4-6" fish, expect that they will be 12-14" long within two years, and plan your initial stocking rate accordingly. Or, consider how many fish you would like to have, and plan to build your pond to accomodate them.

Waste Disposal: Koi, like all animals, follow nature's course - what goes in must come out! This waste material will start to break down, and generate ammonia nitrate in the water - too much, and your fish will get sick and die. Numerous sites provide information on filtration and treatment options, so I won't go into those here except to say that if you are planning to build a pond and have koi, get the best filtration systems you can - a bottom drain for sludge and a biological filter for toxins are tops for maintaining water quality with the least amount of labor, but other options are available if you are willing to put more time and effort into maintaining the water quality of your pond.

Temperature changes: In many parts of the country we can have exceptional temperature swings - especially in the spring and fall! Here in North Carolina we were enjoying 74 degrees last week; yesterday we didn't get up out of the 30's! A shallow pool is more susceptible to these temperature swings, which can be stressful on your koi. In the summer, very warm pond water is also prone to developing heavy algae - which most of us don't want! And you may be in a location where your pond is apt to freeze during the winter. A stock tank heater from your local farm supply will keep an airhole open and help prevent toxic gases from building up under the ice. All of this is to support the idea that your pond should probably be at least 4feet deep, to help buffer temperature changes.

Predators: Blue heron, raccoons, cats - these are probably the most common. Many good suppliers also offer solutions, but one of the first things you can do is to build a fairly deep pond (here's that 4' guideline again!) with straight sides that doesn't offer a good spot for cats or raccoons to fish from, and it's too deep for a heron. A wire around the edge of the pond can discourage herons; a mesh net over your pond may be the solution for all of these. There is also a motion-detector-activated sprinkler that could be installed. And don't think your cat won't get her feet wet - I found out how wrong I was when I went out one morning and found 3 of my favorite koi dead or dying on the ground!

Lastly, consider the swimming health of your fish. A pond that's 8' around may be a nice showplace for smaller fish, but a two-foot koi will not get the exercise it should have swimming in circles. You would be better off with a 16' long pool that's 4-5' wide and at least 4' deep, to provide some straight-line swimming for your larger koi.

For your planning purposes, here is an effective pond volume calculator: http://www.koigarden.com/calc2.php