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Make Sure Winter Koi Pond Care Keeps Fish Healthy

When the water in your koi pond cools down to around 45 degrees in the winter, the fish will chill out near the bottom of the pond, live off their stored fat, and just like the rest of us get ready for spring.

Koi are very hardy fish so they can survive the cold water and ice as long as the pond is between 3 to 5 feet deep, so it won’t freeze solid. But there are some key pond maintenance steps you need to follow to keep them healthy through the winter season.

Keep Water Aerated

Having an aerator running in your koi pond during the winter is the best way to oxygenate the water and reduce ice buildup. Aerators should gently agitate the water without upsetting the pond’s natural balance. The sweet spot you’re looking for is a steady stream of bubbles and you’ll need a small hole or two in the ice for the bubbles to escape. If your koi pond is 4 to 5 feet or deeper, place the aerator in the middle of the depth range (not the deepest spot) so the fish can move to calmer, deeper water if they feel the need to.

Don’t Break the Ice

If thick ice forms on the surface of your koi pond, DON’T just smash it to pieces.  The force of hitting the ice creates shock waves that can injure the koi fish. Instead, use something such as a hot pot right off the stove to melt through the ice. Also, keep an eye on the small holes you’ve made for the aerator and don’t let them ice over. When ice completely seals the water surface the oxygen level drops and creates an unhealthy, acidic environment that will kill the koi fish. Keep in mind that you don’t need to break up all the ice on the pond – it acts as an insulator which is a good thing for maintaining the temperature.

Super Cold Weather? Consider A De-icer (or Two)

Koi fish need a few feet of liquid water throughout the winter so If there’s any chance your pond will freeze solid, you should install a de-icer to keep at least some of the water above freezing. De-icers maintain the water temperature at around 40°F and have a sensor that will shut off the unit when the water hits that temperature. Many koi enthusiasts put two de-icers in their ponds, so they have a backup in case one fails (these also work on a sensor).  If you run two de-icers it’s a good idea to put them on separate circuits, so if one breaker trips, it won't take both units offline.

Don’t Feed Koi During Winter

As the water in your pond gets colder, things start to slow down. Koi stop eating once the temperature gets below 50°F and survive on the fat their bodies put on in the late spring and summer. At this time of year, the koi also need less oxygen since their metabolism has slowed considerably. Essentially, when the water temperature drops, their digestion stops. If they eat it’s often fatal.

Heating Your Koi Pond

One way to battle the icy winter weather is to install a heating system in your koi pond. These are generally made up of a boiler, heat exchanger, and a temperature probe that keep the pond at a steady summer temperature all year long. While this is great for preventing the seasonal temperature swings that can adversely impact koi fish health, remember you’ll need to be out in the cold to keep up on regular feeding, filter cleaning, and other routine maintenance tasks.

At All Bright Aquariums, we’ve been designing and installing gorgeous koi ponds in the Albany, Glens Falls, Plattsburgh, Saratoga NY, and Burlington VT areas for more than 20 years. Give us a call at (518) 307-9291 or reach out online to learn more about how we can work on a design for your koi pond and how our professional staff can handle all the cleaning, maintenance, and upkeep.

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