The Best Guide to Safe Your Koi Pond In Winter

The Best Guide to Safe Your Koi Pond In Winter

Fish are at an increased risk of fish kill when winter months hit. As water temperatures drop, the top of a pond can freeze over. The oxygen supply will be limited, and toxic gasses will be trapped in the water. This can be very dangerous for your fish supply. This Koi pond survival guide details everything you need to do both before and during winter to make sure that your fish survive. 

Preparing Koi Ponds For Winter Months

There are certain steps that you need to take before winter hits to prepare your pond for the winter months. These winter pond prep steps should be completed before the top of your pond starts to freeze. 

Remove Fall Netting

If you installed pond netting to catch leaves and debris during fall, the netting needs to be removed. You should remove your fall netting as soon as the leaves are done falling from the trees. 

Clean All Debris And Leaves From The Pond

Any leaves that are left in the pond will decay. Once they start to decay, they will turn into sludge and release harmful gases. 

Use a long handled pond net to thoroughly clean your pond once the leaves are done falling from trees. 

Treat Your Entire Pond

You don't want to pour chemicals into your pond in winter. However, you do want to treat it before the winter months hit. Koi fish have a poor immune system during colder temperatures. They are not able to handle bad bacteria and parasites as well as they can in warmer months. 

First, make sure that there are plenty of beneficial bacteria in the pond in winter. There are plenty of cold weather bacteria products that pond owners can put in their pond once the temperature on the pond thermometer drops. 

You also need to treat your pond for parasites to winterize your pond. These chemicals are safe for fish and can guarantee that your fish won't die from parasites before Spring hits.

If you have an algae problem, don't try to clean your pond in the winter. The chemicals can be harsh on fish, and stirring up bacteria while removing algae manually from the water can harm your fish. Instead, make sure that you take care of the problem during the Fall months. 

Turn Off The Pond Waterfall

Waterfalls are full of cold water during the winter. If your waterfall continues to run, it will make your pond situation more difficult to manage as the temperatures continue to drop. The water from the waterfall will make the entire pond colder, putting your fish in danger. 

Koi fish are cold blooded animals. That means that they cannot regulate their body temperature. Instead, they rely on the environment around them to do that. They can handle cold temperatures by hibernating, but once temperatures reach freezing the water will start to freeze. Your fish will not be able to handle that. 

Protecting Pond Fish During Freezing Winter Months

As water temperatures start to fall, your fish will naturally begin to use less oxygen and eat less food. They will slowly move to the bottom of the pond to enjoy the warm water that is down there. They can survive like this outside as long as you follow these winter pond management tips. 

Do Not Let The Top Of The Pond Freeze Over

Once the top of the pond freezes completely, harmful gasses are trapped inside, which will kill your fish. You do not need to prevent any ice from forming, though. Instead, you simply need to make sure that there is a hole at the top for gases to escape through. 

Chiseling a hole in the top of the pond is an option, but it's not the best idea. It can scare your fish, especially if they are already in a half-hibernation state. If you can, pick up a pond heater. These are also commonly referred to as a pond de-icer. Thanks to them being controlled by a thermostat, they will kick on as soon as the water reaches a freezing temperature. Then, they will heat up a small circle that will allow oxygen in, and toxic gas out. 


Ensuring that there is proper airflow with an air pump can help your fish survive throughout the winter. An air pump will increase the oxygen level in the water. It will also help circulate the water, preventing toxic gas from settling at the bottom of the pond near your fish. 

Make sure that your aerator is towards the top of your pond for the winter. If the air pump is circulating water at the bottom of the pond it will push the warmer water to the top of the pond. The burst of bubbles coming from your aerator can also scare your fish. When aerators are positioned near the surface of a pond, they help prevent the formation of ice. 

Avoid Feeding Fish If The Temperature Falls Below 50 Degrees

Fish tend to hibernate almost as bears do. Their bodies shut down most of the way, and they tend to be half asleep as they float through the water. Their digestive system also shuts down. Because it is impossible for them to digest food, it's not safe to feed them once the temperature of the water drops. If you do, it can kill them. 

Pick Up A Pond Cover

A pond winter cover can help keep the temperature higher in an outdoor pond. If you own a Koi fish pond, consider covering it throughout the winter along with other methods to prevent your pond from freezing over. 

Heating Your Entire Pond

This is one of the more expensive options to protect Koi fish, but it is definitely effective. Experienced professionals install a comprehensive heating system consisting of a boiler, thermometer, and heat exchanger to raise the temperature of your entire pond. This almost eliminates the need for pond preparation and winter pond care. 

Keep in mind that the larger your pond is, the more expensive this pond setup is going to be. You'll also need to remember that if the water is not cold, your Koi fish will need to be fed all winter long. 

Moving Beloved Koi Fish Inside During Winter

If you do not feel comfortable leaving your fish outside for the winter or are having trouble when it comes time to winterize your pond, consider bringing them inside. Set up an enclosed holding tank, such as a quarantine tank, for your favorite fish, and keep them as indoor fish for the colder months. Pick up an aquarium light to provide them with artificial sunlight, and make sure that the temperature stays above 50 degrees. 

It's important to keep their size in mind. Koi fish grow at a rapid rate. Most indoor tanks are up to 1,000 gallons. You'll also need to purchase equipment for your tank setup, such as a bubbler. Regular fish tanks will not work as a tank setup for Koi fish winter tanks. 

An indoor pond is a more permanent solution. Indoor Koi ponds can be used during winter or they can be a permanent home for your Koi fish. These are created by pouring concrete, and building a pond. Hiring a pond contractor to create an indoor pond is an exceptional idea. 

Creating A Greenhouse

If your entire pond is located outside, you can pick up a greenhouse kit to protect the entire pond from the elements. You can create your own DIY greenhouse with PVC pipe and plastic sheeting or tarps as well. 

However, this will not give you a clean pond or make the water significantly warmer. It offers slight protection against the pond freezing over due to extreme temperatures. Make sure that you follow tips to winterize your pond, keep an eye on your pond thermometer, and clean pond water thoroughly. 

How Deep Do Koi Ponds Need To Be To Survive Winter?

Freezing winter temperatures will not typically kill fish as long as a pond is deep enough. Koi ponds need to be at least 3-5 feet deep for fish to survive. 

What Happens If Koi Fish Freeze?

While some fish can freeze and unthaw, Koi fish is not one of those breeds. If they freeze, they will not survive the winter. 

Do Koi Fish Grow In The Winter?

No, Koi fish do not usually grow in the winter. Koi fish only grow when they are fed. 

In Conclusion

Maintaining your Koi fish pond during the winter can be as simple as an aerator and de-icer or as elaborate as creating an indoor pond. It's important to keep in mind your budget and your preferences. Then, decide which method is right for you and your Koi fish.

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