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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

    Not everyone winterizes (shuts down) their pond. Here at Splash, we usually keep ours running year-round unless we have an especially cold winter. If you prefer the peace of mind of shutting down the pond, though, it’s easy to do.

    Follow the directions below to do it yourself, or, if you live near York, PA, you can contact us to do the work for you.

    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 (optional).

    Pumps and Plumbing

    Check Valve Pond WinterizationIf you turn off your pump in winter, the water that’s usually rushing through your pipes comes to a standstill – putting the pipes at risk of freezing and, potentially, bursting.

    To prevent this from happening, we first need to disconnect the check valve and drain the pipes.

    In most Splash ecosystem ponds, 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 and unthread the top part of the check valve assembly. The small piece still connected to your pond pipe can stay where it is.  You should see the water draining out of your plumbing and back into the skimmer and pond.
    2. Remove the pump and the rest of the check valve assembly from the skimmer and set it next to your pond.
    3. Unthread the bottom part of the check valve assembly, disconnecting it from the pump. This is also a good time to add a lubricant like silicone grease or petroleum jelly to the rubber o-rings.  Store the check valve in a warm, dry place.

    Most pump manufactures recommend storing the pump in water and running it occasionally during the off season.  We’ve found the easiest thing to do is simply place the pump back in the bottom of the skimmer.  Most skimmers are deep enough that the area around the pump won’t freeze solid.  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.  You could also store your pump in a bucket of water in the garage or basement, but this would make quite a mess when running it every other week. 

    Happy Fish

    Pond Deicer


    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.

    While we recommend all pond owners use an aerator year-round, it’s especially important to have one running if you choose to winterize your pond.

    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 de-icer placed on top of the aeration diffuser will help maintain a hole in the ice. A de-icer is a floating heater that keeps the area around it warm enough to prevent the water immediately around it from freezing over. It does not affect the overall temperature of your pond, keeping your fish in their semi-dormant state.

    Most de-icers 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 de-icer. If you live in a warmer climate, or if the winter is 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 de-icer. 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.

    Find an Aerator at our Online Store

    Find a De-Icer at our Online Store

    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.