Nov. 16 2018 06:00 AM

A pond full of fish is a lovely thing to behold, even amid ice and snow. Here’s how to keep those creatures swimming like it’s still summer.


Flashes of gold or orange fish streaking through blue water or maneuvering among reeds in a man-made pond is a magical sight that brings a touch of natural beauty to even the most ho-hum office park or residential backyard. As winter approaches, the koi, goldfish and other types of fish that bring that magic will need extra care and attention to withstand the colder months.

Koi can be a pricey investment. The koi that Mike White, owner of White Water Filters in Batavia, Illinois, sells range in price from $20 to $2,000 apiece. “There are lots of koi in this area that sell for many thousands of dollars,” he says. “Koi in this country have sold for over $100,000. In the world, there have been koi that sold at the million-dollar mark.”

A more budget-minded type can stock his pond with goldfish. White sells them for $5 to $20 each.

But whether he paid $5 or $5,000, no pond owner wants to greet the spring with a pond full of dead fish. As a landscape contractor, your clients may be counting on you to ensure that those entrancing creatures continue to stay alive and thrive during what is, in much of the United States, a few months of extreme cold, ice and snow.

White knows a thing or two about cold winters. The end of October through mid-December is his busy season as he goes about winterizing ponds. His company starts up and shuts down about 150 ponds a year, charging between $150 and $800 to shut down a pond depending on its location and how complicated it is.

Even if you rely on the services of a pond professional like White to winterize your clients’ ponds, it’s good to know what the process entails, so you can help those koi, goldfish and other species stay healthy until temperatures rebound in the spring.

Clean that debris

The procedure for winterizing a pond in a very cold clime is not that much different than it is in a warmer one — but it makes a big difference to the fish who won’t survive without clean water and access to oxygen. “In a warmer climate you don’t have to worry about water freezing over completely, and you don’t have to keep a hole in the ice,” White says.

Even in a hard-freeze climate, fish can stay outdoors in their ponds through the winter, as long as there’s an opening in the ice so they can breathe, and to release gases such as carbon dioxide and hydrogen sulfide generated by decomposing organic debris. These gases, if allowed to build up, are deadly for fish.

“Even though it’s cold, there is still a biological process going on in a pond,” says Dave Jones, owner of The Pond Professional in Woodstock, Georgia. “It is converting organics and breaking them down so they are eventually utilized by plants as food.”

Regardless of climate, warm or cold, whether it freezes or not, all ponds need to be kept clean of leaves and debris to prevent the buildup of toxic gases. Keep trees and bushes near a pond trimmed so foliage doesn’t fall into the water, and keep grass clippings out too.

A pond net placed over the water before leaves begin to drop is an easy way to collect and discard them. Use a skimmer with a long handle to clear leaves and other debris from the pond bottom.

Algae uses up oxygen, so it’s important to get rid of it. Andy Wassmann of Wisconsin Lake and Pond Resource in Eldorado does a final treatment to eliminate algal growth (and also adds a pond colorant).

“Common fish-safe algicides and herbicides are routinely used in ponds that host healthy fish populations,” he says.

It’s not necessary to drain a pond to clean it. “The only time we’d drain a pond would be when it’s a synthetically lined one, so we could pressure-wash it to promote the best possible water quality and clarity,” says Wassmann.

Remove pumps and pipe water

Next, the water pump should be removed so it doesn’t freeze, then stored indoors according to the manufacturer’s instructions.

“Some companies recommend storing them in water, and some prefer they be kept dry,” White says. “The better-quality pumps are stored dry.” All the pads and filter materials should be cleaned with a garden hose and stored.

Another option is to allow a pond to freeze over entirely, remove the compressor and store it in a climate-controlled warehouse. Wisconsin Lake and Pond offers this service. “This allows for easier startups in the spring by reducing moisture damage to the compressor while not running,” says Wassmann.

Irrigation pipes in cold climates need to be cleared of water for the winter, and so do pond pipes, particularly the line from the skimmer to the filtration unit. Any openings in the piping should be plugged at the filter to keep rain or snow from getting into them and freezing.

“The piping is usually flexible PVC, which will tolerate freezing once,” White says. “But the second time it freezes it will shatter like glass.”

Fish need to breathe, even in the winter

A pond can be left to develop a layer of ice on top. As previously mentioned, if there are live fish in that pond, they need to be able to breathe. A hole needs to be maintained in the ice to allow oxygen to enter the water and dissolve. This is absolutely essential.

“By allowing the pond to breathe, you minimize the risk to the fish,” Jones says. “But you don’t want to go out every day and whack the ice with a bat. That causes shock waves that are detrimental to the fish.” A better way is to use a little floating electric pond heater that sits on top of the ice and keeps a circle of it constantly melted.

A small recirculating pump keeps water and oxygen moving. It also helps keep the ice layer thin. “Air stones,” usually pieces of limewood or porous stone that gradually release the air bubbles trapped in them, help too.

Wassmann maintains ponds that are greater than 1/4 acre in size and at least 10 feet deep. His customers have ponds stocked with a variety of species from fathead minnows to largemouth bass and hybrid bluegills. In ponds with established fish populations in both warm and cold climates the company maintains aeration during the winter months.

“For colder climates like Wisconsin’s, if there are four air diffusers in a pond, we will typically keep one of them running during the winter months,” he says.

If there’s a thick layer of ice on a pond, it may be hard to see the fish. But if you notice koi or other fish near the surface, they may be in distress. “If it gets to the point where a koi is ready to die, its instincts will kick in and it will swim to the surface even in cold weather,” White says. “If they are in distress, both goldfish and koi will be at the surface gasping for air.”

Is it too cold for the fish?

The good news is that even in very cold climates, goldfish and koi have a tremendous ability to survive. Both species are hearty and can survive in temperatures as low as 32 degrees Fahrenheit as long as the quality of the water is good, it doesn’t freeze solid and they have oxygen.

In the Chicago area, White says it is common to get 8 inches of ice atop a pond. “Typically, it won’t freeze all the way to the bottom, and fish are smart enough to find a place that isn’t frozen,” he says.

Koi go dormant in cold weather. They will lie near the bottom of the pond to conserve energy and will eat very little. (That’s why it’s a bad sign if you see them near the surface during winter.) Goldfish will continue to swim throughout the season.

Wassmann makes sure any air diffusers are kept out of the deepest areas of a pond. “There is a risk of super-cooling an area where water temperatures tend to remain stable,” he says. “These areas tend to be a common location for fish to overwinter.”

In Georgia, where Jones operates his business, he advises customers not to worry about feeding their koi or goldfish during the winter. “I tell them to let the koi go dormant,” he says. “They’re like reptiles, and can live very comfortably off their body fat. Goldfish also don’t need to be fed because they will find enough food in the pond to live on.”

Some of his customers remove their koi during the winter and place them in a tank inside a heated or semi-heated garage. In that case, “they can continue to feed and grow those fish,” says Jones.

White recommends keeping fish in the pond whenever possible. And, this conveys other benefits. “They’re tremendous at controlling insects,” White says. “They’ll eat the bugs right out of the air, jump up and grab them.”

Should you hire a pro?

Winterizing a pond is a detailed process, and experts have different views as to whether it requires the expertise of a pond professional.

“A pond owner can certainly tackle a winterization checklist on his own,” says Wassmann. “Any mechanically inclined individual would be able to handle the compressor maintenance as well. But all the items on the list must be completed to prevent fish kills and equipment damage.”

White says, “It depends on the pond. Most homeowners don’t have the equipment or the knowledge to shut a pond down correctly.”

For Jones, hiring a professional to winterize a pond is cheap insurance against broken equipment or worse, dead fish. “While a professional is there he can look at the entire system and see if there are any problems,” he says. “It’s better to be preventive rather than reactive.”

Everyone — the landscape contractor, the pond professional and especially the pond’s owner — wants to see happy, thriving swimmers when spring finally does roll around. Sadly, Jones says he’s handled too many cases where just the opposite happened. “I keep saying I’m going to get a T-shirt that says, ‘My fish are going to be so happy once I get it all figured out.’ Unfortunately, the fish pay for people’s learning curves and mistakes.”

This need not be your fate. If you’re a landscape contractor who has clients with ponds and you want to gain knowledge about their workings, Jones recommends connecting with an experienced expert.

“Hook up with a seasoned professional who’s willing to give you some sage advice,” he says. “I make my living off of fixing other people’s mistakes, whether they’re pros or do-it-yourselfers.” Hopefully, these tips will prevent you from making those kinds of errors.

The author is a Chicago-based freelance writer who covers business, technology and the environment.