How to Winterize Your Koi Pond

The temperatures are dropping and your pond is covered in a beautiful icy glaze. Your fish are nestled in for a nice winter’s nap.

But your pond ecosystem still needs a little help to make it through the subfreezing weather.

You need to consider two critical factors when preparing your pond for winter:

  1. Protecting your pipes, pumps and plumbing
  2. Keeping your fish happy and healthy

At a Glance: How to Winterize Your Pond

  • Unplug your pump and drain your plumbing.
  • Place an aerator about 10 to 12 inches below the water’s surface.
  • Install a deicer.

Pumps and Plumbing

Check Valve Pond WinterizationThe first step to winterizing your pond is disconnecting the check valve.

The check valve assembly is an L-shaped piece of plastic pipe inside your skimmer that connects the pump to the rest of your pond plumbing. This structure holds the water in your line during the season, which is why you need to remove it in the winter.

Disconnecting the check valve assembly is easy:

  1. Unplug the pump.
  2. Unthread the top part of the check valve assembly. The small piece still connected to your pond pipe can stay where it is.
  3. Remove the pump and the rest of the check valve assembly from the skimmer and set it next to your pond.
  4. Unthread the bottom part of the check valve assembly, disconnnecting it from the pump.

Store the check valve in a warm, dry place, and place the pump back in the bottom of the skimmer. To increase longevity of the pump, plug it in and run it occasionally throughout the winter; a few seconds every other week is usually sufficient.

Happy Fish

Pond Deicer


Although we love to see and hear our waterfalls all year long, for the most peace of mind, we recommend turning off your pump in the winter. When you do that, however, the water that’s usually rushing through your pipes comes to a standstill – putting your pipes at risk of freezing and, potentially, bursting.

In the winter, koi and goldfish enter a semi-dormant state called torpor. It’s not quite hibernation, and they are still living and breathing.

While they do not need food when water temperatures are below 55 degrees, they are still exhaling gases that we need to get out of the pond. Disturbing the water surface with a waterfall or a pond aerator as the temperatures drop below freezing is critical for fish health so those gases don’t get stuck under ice.

An aerator consists of an air pump that sits next to the pond and a weighted diffuser that goes in the pond and blows out tiny air bubbles. An air hose connects these two pieces.

Place the diffuser about 10 to 12 inches under the water’s surface. Don’t put it in the deepest part of your pond; if you do, the air bubbles won’t be able to disturb the water’s surface enough to prevent ice from forming.

Koi Pond Aerator

Aeration Kit

In case of extreme cold, a pond deicer placed on top of the aerators will help maintain a hole in the ice. A deicer is a floating heater that keeps the area around it warm enough to create a hole in the ice. It does not affect the overall temperature of your pond, keeping your fish in their semi-dormant state.

Most deicers are thermostatically controlled, meaning they automatically shut off when the water around them reaches a certain temperature.

Not all pond owners choose to use a deicer. If you live in a warmer climate, or if the winter is especially mild, you might not need it. If you do decide to use one, it should be in addition to the aerator, not in place of it.

For the most peace of mind, especially if you spend part of the winter away from your pond, we recommend installing an aerator and a deicer. If the power goes out, the deicer will still disturb the water’s surface as it floats on top of the pond, giving you a safety net if the aerator stops working.

Learn more about keeping fish happy in our Ultimate Guide to Pond Fish Care.

More Winter Pond Tips

  • Switch to cold water fish food in the fall, and stop feeding entirely when the water temperature is consistently below 55 degrees. Here’s why.
  • If your pond freezes over before you have a chance to winterize it, gently make a hole in the ice. Read our tips on how to do this without harming your fish.
  • Schedule your Spring Pond Clean-Out while the water is still cold. Cleaning your pond before the water warms up gives your beneficial bacteria colonies a chance to thrive.
  • Keep an especially close eye on your pond during extreme cold temperatures.
  • Don’t add salt to your pond in the winter.  Salt lowers the freezing point of water.  If the water temperature at the bottom of your pond drops below 34 degrees, the cold could injure your fish’s gills.