Winter Pond Maintenance: How To Protect Your Pond And Fish

Keep Your Pond And Pond Fish Safe During Our Freezing Maryland, DC, And Northern Virginia Winters

Winter pond maintenance can be the difference between having a pond in the spring or having a half-dead swamp in your yard. Taking care of your pond and koi fish during winter involves cleaning, not feeding your fish, keeping a hole in the ice, and more. You can read about our winter koi pond care process so you can know how to best care for your pond and pond fish when it’s freezing and snowing.

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Winter pond maintenance can be the difference between having a pond in the spring or having a half-dead swamp in your yard. Taking care of your pond and koi fish during winter involves cleaning, not feeding your fish, keeping a hole in the ice, and more. You can read about our winter koi pond care process so you can know how to best care for your pond and pond fish when it’s freezing and snowing.

Winter pond with aeration and ice hole

Will They Become Fish-cicles?!

“I’m honestly kind of scared for our koi fish and our pond, dear.”

Amy’s watching the weather forecast and it’s starting to dip down into the freezing temperatures in the next week or so. She and her husband, Will, recently had a koi pond installed in their back yard.

Close up of large koi pond and koi fish

Now they’re worrying about what to do if it freezes over. “Will our koi become fish-cicles?!” Amy asks, voice rising with concern.

Will suggests looking online to see if they can find any steps for winter pond maintenance and winter koi fish care. The first few results are for winter pond maintenance services, but then they find an article that has tips and steps for it.

7 Steps To Winter Pond Maintenance

  1. Remove any fall netting
  2. Clean your pond and filters
  3. Shut down the waterfall or make sure it’s winter-ready
  4. Move/place an aerator 1 foot below the surface
  5. Turn off automatic pond parts like Ion-Gens and autofill devices
  6. Add a de-icer when your pond freezes (don’t break a hole)
  7. Remove pump and store in water if you shut down the pond
  1. Remove any fall netting
  2. Clean your pond and filters
  3. Shut down the waterfall or make sure it’s winter-ready
  4. Move/place an aerator 1 foot below the surface
  5. Turn off automatic pond parts like Ion-Gens and autofill devices
  6. Add a de-icer when your pond freezes (don’t break a hole)
  7. Remove pump and store in water if you shut down the pond
Partially frozen waterfall

The couple feels slightly at ease knowing that the hardest part of winter pond maintenance is cleaning the pond and filters. They aren’t sure if they should leave their pond running or shut it down.

Mostly, it’s up to how much work you want to do if you’re deciding between shutting your pond down for winter or not. If you keep it running you’ll want to keep an eye on it to make sure ice dams don’t form and send water shooting into your yard. If it does you’ll have a swamp for a yard when the snow melts.

The couple decides to leave their pond running because the article says they can get some beautiful ice formations from the water.

But Will wants to know the reason behind some of these steps.


The Reasons Behind These 7 Steps

Cleaning the pond and filters gets rid of the muck and debris at the bottom of your pond. Anything left over winter will break down and release gases into your pond.

These gases (and the ones from your hibernating fish) are toxic when enough of it is trapped, which is what would happen if you didn’t keep a hole in the ice with your waterfall or de-icer. The hole also allows fresh air to enter the pond.

For your fish, breaking a hole in the ice would be like you being half asleep and a giant hammer suddenly crashes through your ceiling. It’s scary and can hurt or kill your fish.

Using aerators to form a hole in the ice for winter pond maintenance

The aerator moves oxygen around but you must absolutely move it to the shallow end. If left in the deep end it’ll send warm water up and cold water down, leaving your fish stuck inside the cold.

The automatic pond parts like the Ion-Gen (what’s an Ion-Gen?) aren’t needed during winter so you can turn them off. Storing the pump in water keeps it in better condition.

Amy’s more concerned with how to care for koi fish during winter. What winter pond maintenance steps do they need to know for koi fish?

Can Koi Fish Survive Winter In An Outdoor Pond?

Koi fish can survive winter in an outdoor pond if your pond meets certain standards. The pond needs to be at least 2 feet deep and cleaned. You’ll also need to have an aerator in the shallow end and a de-icer keeping a hole in the ice.

Under 2 feet the water shouldn’t freeze.

Koi fish under ice is fine because winter pond maintenance was performed

Do not feed your fish under 50°F. Their stomachs and digestive system slows down to the point where the food will sit there and that can hurt or kill them. It’s like the world’s worst stomach ache. You can switch to cold temperature fish food when temperatures are between 60-50°F

But what’s the pond maintenance process if the couple wants to move their koi fish inside during winter?

Moving Koi Fish Inside During Winter

Moving koi fish inside during winter involves:

  • Using de-chlorinated water in a 100-1000 gallon tank
    • Polytank or stock tanks are stronger and easier to move than glass
  • Putting the tank near a power and water source, and drain for easier cleaning and filling (weekly)
  • Setting up a small filter, aerator, and de-icer 
    • If the area is heated then get food instead of the de-icer
  • Cover the tank with a net so the koi don’t jump out
Koi fish in a tank during winter

Will doesn’t want to do this and they don’t have to because their pond can support their koi fish during winter. 

Amy’s thankful they found this out before winter set in, otherwise, they’d have to follow a slightly different winter pond maintenance process.

Preparing A Koi Pond For Winter When Winter’s Already Here

Go ahead and leave your pond running. Make sure it stays full so the pump doesn’t try to run without any water. Make sure to check for ice dams or you’ll have a swampy yard!

If it’s frozen then get a de-icer on it ASAP! De-icers are great for many reasons, like keeping you from trying to break a hole in the ice. Do not break a hole in the ice. Then move/put an aerator in the shallow end.

After that, there isn’t much you can do besides keep an eye on it and your fish.

Let’s Do It!

Amy and Will now have to talk about whether or not they’ll try to maintain their pond on their own or hire someone to do it. The only real problem is the cleaning part… Well, they want their pond and fish to be safe, plus the better the winter maintenance is the better spring maintenance will be too.

You can download our guide to spring pond maintenance and get a head start >>