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Harsh Winter Fish Kill?


I have received more questions like this one below this year than ever before and asked Aquascape Tech for their response.

Frozen turtleQuestion:

“I lost a lot of koi this winter because of extreme cold conditions, thought I had enough aeration and de-icers apparently not  would like alot more info on how to prepare better for harsh conditions”

Aquascape Tech Answer:

“Hhmmm that is kinda of hard to answer with no information from that person. 

I think the best response is that this was an extremely unusual winter and the even the Department of Natural Resources has issued a statement that they are expecting to see large fish losses in natural stream and lakes due to this year’s extreme weather.  Aquascape will be reviewing their winterization suggestions, but sufficient aeration, and openings in the ice usually work.  When you have the 3rd harshest winter in 150yrs (Chicago) it is difficult to predict all possible scenarios.  

Low stocking levels and having healthy fish heading into winter is also beneficial.  If the fish are stressed going into the winter months they are even less able to handle a severe winter.”

The PondMeister’s Normal Answer:

“The fish are fine in freezing weather. It is not the cold that kills the fish – it is the gasses trapped by a frozen over pond that kills the fish.

The 3 ways to keep a hole in the ice are: 

1.            De-icer – These keep a hole in the ice allowing the gasses to escape

2.            Pond Aerator – A pump which sits outside the pond and pumps air into the water. The bubbles keep a hole in the ice

3.            Submersible Pump at Water Level – The bubbling effect of the water keeps a hole in the ice. 

In extreme winter areas, some people chose to select 2 or 3 of the above in case one method fails.

Of course once the water temperature drops below 55 degrees there is no longer any need to feed the fish as their digestive systems are unable to digest the food.”

Frozen pond


I thought Aquascape’s response was a great answer and illustrates that even if we take every precaution, sometimes our best efforts may not be rewarded.

Nature can be BRUTAL!

date Posted on: Wednesday, March 19th, 2014 at 4:31 pm
Category Pond News.
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  • Barb

    Winter was extreme in PA also this year. I prepared my goldfish with the Spring/fall diet. I used an aerator and a floating heater. My ponds only about 26″ deep. The aerator got covered in ice many times but it made some interesting volcano looking projections up from the ice. The heater did keep an opening. We went into winter with the cleanest pond we could free of leaves and debris. As Winter waged on I was so fearful my fish could not make it. The 6 adults are 3 years old and the babies were from Summer. It’s March 20th now and the ice has thawed. Last count I still have 6 large goldfish and my 10 babies. How they made it is beyond me! I even had to buy a Heron decoy because we had a very large Heron visitor this winter also. Looking forward to Spring clean up and my babies coming up to see me!

  • fred

    This is an easy one! Keep your waterfalls going all year and install a 300 watt pump heater to keep a hole in the ice to let gasses out. I also put a 2″ pvc pipe with curved end adapter on both ends and put it down to the gravel on the deep end of the pond coming above the water about 3′. also, MAKE SURE YOUR WATER IS DEEP ENOUGH – 3′ minimum at the deep end so fish don’t freeze in the ice. The water will keep moving under the ice to the skimmer with the pump running to the water falls.

  • Kent

    Years ago, I got frustrated with the floating de-icers (heaters) as they failed quickly and just sucked up a lot of power and evaporated lots of water.
    My pond is just under 4 feet deep in the center. I used a cheap $10 or less aquarium aerator and stone. I took a heat tape and ran it through a conduit (flexible split-tube wire organizer) with the air tube and led the stone and the excess heat tape to the bottom of the pond.
    The pump is on a timer to be on for an hour a day (around noon-1, when its warmest out).
    The theory I went on was that ICE IS GOOD! Ice insulates the water. The small bubbler does a good job removing gasses, without over circulating the water and causing it to cool too much.
    Since I went with this method my winter fish kills have been virtually non-existent. Even last winter when I could hear “frost quakes” as the ground froze solid, we had no deaths to report in the spring.
    I don’t worry about thick ice or snow buildup. Even if the bubbler cannot make a hole in the ice, it is still forcing air down there, which will remove the gasses from the water. It will find its way out somewhere – often around the edge of the pond if frozen too hard to make a hole above the air stone.
    Fish: Gold Fish
    Pond: Approx 8’x8′ average depth 24″ with 2’x3′ 46″ deep spot.