How to Properly Winterize Your Koi Pond

Select Koi Inc
Oct 30
3 min read

As temperatures drop, your koi slow down — and your pond’s ecosystem changes right along with them. Proper winterization is essential to keep your koi healthy, and your water balanced through the cold months. Whether you’re in Tennessee or further north, a few key steps can protect your pond (and your investment) all winter long. Taking the time to winterize your koi pond properly not only keeps your fish healthy — it ensures your filtration system and pond structure stay protected. With just a few preventive steps, your koi will greet spring healthy, active, and ready for another vibrant season at the surface.

Lets Break It Down…

Step 1: Deep-Clean Before the Chill

Step 2: Trim and Tidy Plants

Step 3: Adjust Feeding and Monitor Behavior

Step 4: Maintain Oxygen and Water Circulation

Step 5: Clean and Check Equipment

Step 6: Add Beneficial Bacteria

Final Tip: Observe, Don’t Interfere

Step 1: Deep-Clean Before the Chill

Start by giving your pond a thorough cleaning. Remove fallen leaves, sludge, and excess algae buildup so that decaying organic matter doesn’t affect water quality during the months when your biological filtration slows down.

Pro Tip: If your pond is large, use a pond vacuum or perform a partial water change while cleaning.

Step 2: Trim and Tidy Plants

Cut back hardy plants to just above the waterline and remove any floating plants entirely. This prevents rot and debris buildup that could deplete oxygen levels over winter. Finish by covering your pond with a pond net or breathable cover. This prevents debris from entering, deters predators, and helps maintain a stable temperature through the coldest nights.

Step 3: Adjust Feeding and Monitor Behavior

As the water temperature drops below 55°F (13°C), your koi’s metabolism slows dramatically. Gradually reduce feeding, switching to a wheat-germ-based food, and stop completely when temperatures stay under 50°F.

Uneaten food in cold water can quickly spoil and pollute the pond.

Step 4: Maintain Oxygen and Water Circulation Ensure proper oxygenation by using a de-icer or aerator prevent the surface from freezing over completely.

Other crucial steps include adding beneficial bacteria, cleaning filters, and covering the pond with a net to prevent debris from entering. More on this below.

If your region experiences freezing temperatures, consider installing an inverter system or low-wattage pond heater to maintain consistent power to your filtration or aeration equipment.

This ensures that oxygen and water flow remain stable without spiking energy use.

Step 5: Clean and Check Equipment Before shutting down your main pump or filter for the season, clean all filter pads, skimmers, and tubing.

If you’re leaving equipment running, make sure it’s operating at reduced flow and that intake pipes are deep enough to avoid drawing in frigid surface water.

Step 6: Add Beneficial Bacteria

Even in cold water, specialized cold-weather beneficial bacteria help maintain water clarity and break down organic waste.

Add a dose after cleaning and again mid-winter to keep your pond balanced.

Final Tip: Observe, Don’t Interfere

Once your pond is winterized, it’s best to observe rather than intervene.

Avoid breaking ice with force (which can shock koi) and resist the urge to feed them until spring temperatures stabilize.

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