Keeping Koi

A Fishy Love
by Stevie Sigan

Koi enthusiasts fall for the colors, scales and fins, but it’s not all fun and fishes. Still, the time and toil required to keep up a koi pond is well worth the effort.

It all started with a hard plastic preformed pond liner—the same way most people start out, recalls Vincent Smith, director of the Peoria-based Prairieland Koi & Pond Society. After installing it in his yard, he got “a little pump, circulated some water, stacked some rocks around it, threw in some feeder goldfish,” and was well on his way to a life of koi.
Smith makes it sound easy. But maintaining a koi pond requires a commitment to a species with elaborate water needs, plans for handling their likely offspring, and the ability to defend against looming predators.

Snow White, Cherry Red
Bred as designer fish for their hearty nature, koi, or “carp” in Japanese, are believed to have come from western Asia or Persia. They were eventually introduced to Japan, where breeding the versatile species, also known as nishikigoi, for their “brocade, fine dress and splendor of color” caught on quickly. Breeders began harvesting different colors and variations and keeping koi as pets in the 1800s, and in 1914, the colorful carp was first showcased nationally at the Tokyo Taisho Exhibition. Its beauty proved contagious. Today, they are commonplace in backyard gardens and landscapes throughout the world.

Larry Zehr, president of the Prairieland Koi & Pond Society, has devoted his life to the fish, breeding conventional and butterfly koi in his interconnected, four-pond “chain of lakes,” keeping the premium-grade adult fish in the front two pools and the babies in back. With each spring comes a flurry of eggs, and Zehr places “weeds and plants in the shallow area for the eggs to stick to,” relocating them to the “baby pond” once they are laid so that the adults don’t eat them. They hatch within three to five days, leaving him with “hundreds of quarter-inch babies.”

Like a proud father, Zehr boasts of his seven regular koi, 10 butterfly koi and his "babies,” which he’ll start to sell once they’ve grown a bit—the longer they are, the higher the price. “People come from quite a ways to buy them,” he explains. “The most expensive ones are cherry red and snow white. It’s hard to get them that perfectly red. I have one that’s just gorgeous—it’s from Japan—a white fish with two big red spots…and sparkling scales.”

The butterfly koi are a customer favorite. “[They] have very fancy fins that are quite a bit longer than conventional koi, so…they’re a whole lot prettier. And of course, they’re quite a bit more money,” says Smith.

Zehr waxes poetic as he describes the different colors, fins and reflecting scales, “some with ridges in them like a diamond… We’ve got red koi and white koi and blue koi…they come in every color, really,” he says. “The metallic ones really stand out. The white ones glow silver…”

Smith shares Zehr’s passion: he and his wife are constantly falling in love with the different colors and varieties, always wanting to add more to their pack. “I think we’ve reached our magic number in terms of big fish, though…because you can put too many fish in a pond, and that’s not good for them.”

Clean, Cool & Aerated
Maintaining the water’s oxygen level is vital to creating a healthy environment for koi. When it gets too crowded—most guides recommend a half inch of fish for every square foot of water surface area—there’s less movement, and less available oxygen. With the right amount of filtration and aeration, more fish can be kept in a smaller space, but one must be wary. “As long as you’re moving the water, you’re providing aeration,” Smith says. “But if there is a power outage…and your pond just sits there for, say, three hours one afternoon, and you have way too many fish…they’re all going to be up at the surface trying to get oxygen,” he says.

There are many classifications of koi, and varieties nested within varieties. Here are a few of the main ones:

Kohuku. One of the most common varieties, kohuku are white koi with red markings.
Sanke. Red and black markings on a white koi
Showa. Red and white markings on a black koi 
Bekko. White, red or yellow koi with black markings
Asagi. Blue-gray koi with red sides, underside and fins
Koromo. Koi with a red pattern like a robe, outlined in a darker color
Hikarimono. Single-colored, metallic koi
Kinginrin. Koi with more than 20 sparkling scales.


One of the things Smith had to get accustomed to during his first pond operation was keeping three quarters of the pond covered in water lilies. “I’m going, ‘Well, if I do that, I can’t see my fish!’” he exclaims. Now, he equates the beauty of the landscape to that of the koi. “As long as your pond’s in the sun, then the water lilies have blooms…that adds to the color and beauty of it all.”

The lilies work wonders for the water’s quality and temperature as well. Shading the water, they maintain a slightly cooler temperature, especially helpful in the summer, and offer a place for the fish to hide, making it harder for predators to know they’re swimming below.

But unlike the lilies’ lending cover, leaves can be a problem. Netting is often placed over the surface to prevent them from falling in and producing tannic acid as they break down. (The tannins can cause yellowing and make fish more vulnerable to disease.) The main koi pond at the Peoria Zoo, installed by the Prairieland Koi & Pond Society in 2001, requires a thorough leaf cleanup each spring, Smith explains. The pond contains about two dozen koi and is nicely landscaped, thanks to Society volunteers.

In spite of the challenges, all that attention to detail really pays off, Smith says. His home pond, which he started in 2002, now contains some koi over 10 years old. “If you get the environment right,” he says, “I’ve been told they can live 60 to 70 years.”

Long Winters & Long-Legged Birds
Unless you plan to transfer your fish indoors each winter, properly “wintering” your koi is yet another challenge. Because the warmest water during winter is at the pond’s very bottom, once cold temperatures have set in and there’s ice on the surface, it’s important not to cause too much circulation in the water—as stratification ensures the koi don’t freeze. And yet, the fish must also continue to receive oxygen via an opening through the ice. Therein lies a difficult balance: an aeration device must be kept to the side of the pond to allow for oxygen exchange without disturbing the layers. While complicated, it’s worth the extra precautions to keep them outside, says Smith, who doesn’t like “putting the fish through any more stress” than necessary.

A more serious threat than the winter’s frost, Smith and Zehr agree, comes from above. “We’re close enough to the Illinois River that the blue heron will on occasion fly off the river and find someone’s pond,” Smith says. “Blue heron, of course, like to eat fish. They will find your pond and decide to stay until they empty [it].”

Zehr lost a three-pound beauty to a monstrous heron a few years back. “I’m 5’6”, and I looked up to it!” he exclaims. Likewise, Smith sat out by his pond one night and noticed a heron hovering in a nearby tree. “His wingspan was as big as my arm span!”

Because it is federally protected, there is little that can be done when a heron arrives. “You walk out and see this four-foot tall bird standing in your pond, and what can you do? You’re not supposed to hurt them,” Smith explains, “but you don’t like to lose fish you’ve had for 10 or 15 years.”

After that initial sighting, Smith began a nightly watch before resorting to other protective tactics. He strung clear nylon fishing line in a zig-zag pattern across the water’s surface to deter birds from landing and even tried rigging a clock radio to a motion detector, so “if any movement happened around the pond, it would turn the radio on and hopefully scare them away.

“I didn’t think it was going to be too effective until the first night I walked out…and got close enough to the sensor to set it off, and gave myself a start,” he laughs. “Well, hopefully it will work on the bird, it just did me!”

Fin-Wagging Company
Off watch duty at the end of a long day, Vincent Smith perches on the swing beside his backyard koi pond. Thirteen fish wag their fins toward his presence at the water’s edge, awaiting food. Smith’s dog drools idly by, hoping for scraps of the taupe-colored packed protein pellets.

“The koi can see you,” he explains. “They get used to you...[and] you can actually teach them to eat out of your hand.” His yard is a dense, carefully detailed landscape of bushes and grasses, flowers and trees—evidence of his wife’s love to “get her hands dirty and…dig in the dirt.” Her passion for gardening dovetails well with their shared koi hobby. Today, the 2,000-gallon pond takes up the majority of their yard—nearly 15 times the size of that original hard plastic liner. 

“Just like any other hobby, you’re going to put some money into it,” he says, sitting beside his pond. “It is some work, but it’s a good way to reduce stress and make your day a whole lot better.” a&s


Don’t know where to start? Consider this brief overview for beginners, or read the full guide at

  • Decide where to put your pond. A mostly shaded area is best, although a bit of sunshine (4 to 6 hours a day) will encourage water lily blooms. Choose a location that does not permit rain runoff to flow into the pond, and avoid placing it too close to trees.
  • Plan. Be sure your plot doesn’t have any underground pipes—the depth of a koi pond is ideally five feet (or at least three), with at least 1,000 gallons. Remember that a larger pond is more stable and easier to maintain. Sketch a plan and measure dimensions before buying anything. Decide if you will install it yourself or hire a contractor.
  • Purchase a pond liner once you know the dimensions. You’ll also need the right-sized water pump to run a filter. 
  • Dig! Consider shelf depths—you’ll want to cascade the pond so it’s shallower on its sides and deepest in the center. Don’t forget to dig a ditch for the plumbing from the pond to the (optional) waterfall or external filter. If you plan to line the sides with plants, include a foot-deep perimeter surrounding the pond.
  • If you are using a pond underlayment, lay it down first. This will further protect the rubber. Then, place the pond liner and unfold, minimizing wrinkles. 
  • Edge the pond. There are several methods of doing this, from natural-looking layered stone to basic thin stone. 
  • Add the water and dechlorinator to remove any chlorine or chloramines.
  • Choose and add your aquatic plants. Anacharis, water hyacinths and bacopa are a few good choices. Water lilies will offer added shade and shield for the fish. 
  • Turn on the pump/filter. A packaged bacteria can help seed the filter and maintain a clean, healthy pond. Use it regularly for a few weeks before adding the fish. 
  • Add your fish, keeping in mind the formula: half an inch of fish for every square foot of water surface area. Ideally, they should be added a few at a time over several weeks.