Home Improvement Expert Danny Lipford

How to Keep Koi Fish in a Pond During Freezing Weather

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During this latest cold snap, my koi fish pond has threatened to freeze over. What should I do? -Brett

Ice by itself is not dangerous to koi, as long as your pond is deep enough not to freeze completely (3-5 feet or more). The danger to fish comes with the reduced oxygen and increased toxic gases caused by the sealed over water surface.

While you could move your fish and plants to a temporary indoor tank for the winter, or install pond heaters that use a lot of energy, in many cases you can overwinter your fish outdoors with a little care. Keep in mind these tips:

  • Aeration: Have an aerator running in your pond at all times to keep the water stirred and promote the exchange of gases. An aerator is a lot more economical than a pond heater, and it will oxygenate the water while reducing ice build up.
  • Ventilation: If you’re aerating the water, all you need is a small hole or two for the bubbles to escape. You don’t need to remove the rest of the ice from the surface.
  • Balance: Koi (and many other fish) go into a sort of dormancy in the winter, using less oxygen and naturally settling to the bottom of the pond where the water is warmer. Your aerator should gently stir the water without upsetting this natural balance. Go for a steady stream of bubbles, not a rolling “boil” or strong current. If your pond is 4-5 feet or deeper, put the diffuser at the middle of the depth range (not the deepest part) so that the fish can retreat to less-disturbed deeper waters if needed.
  • Ice: Don’t break the ice in your pond by hitting it, since the force can cause shock waves that may hurt the fish. Keep an eye on your ventilation hole and remove any thin ice before it becomes thick and hard. If necessary, you can sit a full, hot teakettle on top of the ice until it melts a hole. Otherwise, let it snow! The snow, ice, and surrounding earth will help insulate your pond from the frigid air.
  • De-Icer: If your pond threatens to freeze completely, you may need to install a de-icer to keep at least part of the water above freezing. Your fish will need a few feet of liquid water in the pond throughout the winter.

Further Information

Julie



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4 Comments on “How to Keep Koi Fish in a Pond During Freezing Weather”

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  1. Alan Deacon Says:
    January 25th, 2010 at 11:00 am

    These are excellent tips. Many people don’t know how to take care of their koi winter pond. Besides the winter care they need to know how to prepare their pond for the winter months!

  2. Lesley Says:
    January 5th, 2013 at 6:01 pm

    HI There

    I have a koi pond that has a waterfall (which we turn off during the winter) and the pond is deep enough that we dont have to bring our 10 koi inside. We also use a bubbler pump during the winter but we still have a hard time keeping the pond from freezing over we had to build a cube around it which helps but it still freezes over (well it forms like a ice globe over the bubbler) is there anything else we can do to stop it from freezing over??? should we build snow hills against our cube (made out of thick styafoam) or what?>

    Help@!

  3. Robert casale Says:
    January 31st, 2013 at 3:44 pm

    Hi. I seem to be having a problem with my heater for my koi pond. It did the same thing last year so I went out and bought a new one. It’s doing the same thing. It goes red for a while when it gets cold but now it just stays green. Why is this happening? Is there something I the water that’s affecting my heater? Is it some thing to do with my electrical outlet.

  4. Mrs Hughes Says:
    September 19th, 2014 at 5:29 am

    Thank you all for these tips, I have a pond with goldfish in and it is my first year. Now I know about frost and think I can protect them what do I do about feeding/not feeding them? I heard that they don’t need feeding in the winter but when and how do you stop?
    Thank you in advance for any replies

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