How to Protect Your Koi Pond in the Winter

Updated Oct. 2021

If you recently installed a koi pond and have concerns about protecting your fish during the winter months, there are a few things you should know. Koi are resilient fish and can survive in outdoor ponds during harsh winter conditions, which means you do not need to bring them inside for the winter. However, they can only survive a freezing Illinois winter outdoors if you properly protect and maintain their home.

As long as your koi pond is between three to five feet deep, you should not need to worry about your pond completely icing up in the winter. This depth leaves plenty of room for your fish to swim around at the bottom of the pond even if the surface of the pond freezes.

However, if your pond and fish are going to make it through the frigid Midwest winters, then you’ll want to provide extra care and maintenance. Here are a few things you can do to protect your koi pond during the colder months.

Keep Your Pond Aerator Running

It’s important to have an aerator running throughout the year and not just during the winter, but an aerator is essential during the winter and costs less than running a heater.

Aerators keep oxygen flowing through the pond, prevent ice from building up, and promote the circulation of nutrients and food for the fish. Overall, aerators improve the quality of the water, creating a more comfortable environment for your fish.

Install a De-Icer

If your pond is less than three feet deep, you may want to install a de-icer to keep part of the water from completely freezing. Your koi fish need at least a partially unfrozen pond if they are going to make it through the winter.
 
A de-icer can also keep ice from damaging components in your pond should you choose to leave them in there during the winter. Keep in mind that once you get below freezing, any items in the water can break easily due to the expansion of the ice. Therefore, it is still a good idea to remove as many items from your pond as possible, leaving only those components that are essential for the health of the pond.

Do Not Attempt to Break the Ice

One of the biggest mistakes you can make is to attempt to break up the ice that forms on the surface of your koi pond. Breaking the ice can harm both the fish and any components in the pond.

Rather than breaking up the ice with a hammer or other tool, we recommend using an auger to drill holes in the ice. This allows the air to pass through the ice, releasing any harmful gasses that may have built up. 

After you have made holes in the ice, make sure your aerator is gently stirring the water so air bubbles can find the holes and release any necessary gasses. In addition to venting gasses, this process keeps cold air from accumulating under the water and creating more ice.

Tips on How to Look After Koi Fish and Pond During Winter

Winter can be a challenging time for koi fish and their ponds. Proper care ensures their health and the pond’s ecosystem remains balanced. Follow these essential tips to keep your koi fish safe during the cold months.

1. Monitor Water Temperature

Koi fish thrive when the pond’s temperature stays within their tolerance range. Use a pond thermometer to ensure the water doesn’t drop below 39°F (4°C).

2. Adjust Feeding Habits

Koi fish metabolism slows down in colder temperatures. Switch to a low-protein wheat germ-based food and stop feeding when the water temperature falls below 50°F (10°C).

3. Maintain Proper Oxygen Levels

Ensure adequate aeration by using pond de-icers or air pumps to keep a small part of the pond surface ice-free. This allows oxygen exchange and prevents harmful gas buildup.

4. Clean and Prepare the Pond

Remove debris like leaves and organic matter to prevent decomposition, which can reduce water quality.

Prepare for the Upcoming Cold Season

In addition to creating a healthier environment for your koi fish during the winter, there are also some things you can do to prepare your pond for winter and for the drop in temperature, such as:

• Gradually transition from using summer food to feed your koi fish to winter food during the fall.
• Clean your pond and remove debris in and around the water.
• Add netting over the water to prevent additional debris from getting in the pond.
• Add cold-water-beneficial bacteria and enzymes to your pond to break down organic materials.
• Remove the water pump, filter pads, waterfall equipment, and UV lights from your pond and store them in a safe place during the winter.

Once spring returns, you will want to perform a thorough inspection of the pond for any damage. You will also want to clean the pond and return all the equipment that you removed.

Care Aspect	Action to Take	Why It’s Important
Water temperature	Monitor with a thermometer	Prevents freezing and stress for koi fish.
Feeding	Switch to low-protein food; stop below 50°F	Avoids overfeeding and health issues.
Oxygenation	Use de-icers or air pumps	Maintains oxygen levels and prevents ice buildup.
Pond cleaning	Remove debris	Improves water quality and reduces toxins.
Temperature regulation	Use heaters or covers	Ensures stable conditions for koi fish.

Complete Koi Pond Design and Installation

If you are ready to build your koi pond, Reflections is here to help. We offer a wide range of features and options to help you create the perfect, serene pond or natural pool.

To find out more about our products and services, contact us today at (815) 955-4911 for a consultation.

Quick Links on Pond In Winter Question

Keeping Your Water Garden Healthy in Winter
How to Care for Your Koi Fish and Pond in Winter
How to prepare natural pools and koi ponds for winter
How Koi Ponds Are Designed and Constructed