All my Large Koi died over winter, Why?


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I had 6 large koi and 7 smaller ones in the fall. I placed 2 of the donut heaters in the pond, as I do every year. Well, we had a very cold and snowy winter but, they still died this winter. Can some give me some idea on why this happened? Thanks.
 
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Most likely it was because of lack of oxygen.
Floating heaters are borderline effective, and if they were ever covered by snow and ice, even temporarily, the fish could have run out of oxygen.
It depends on a lot of factors.
 
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@carmine160 - I'm so sorry to hear that! We had a similar event this year, but ours was due to the pump plumbing failing at a bad time and having our waterfall shut down during a polar vortex here in the midwest. Very sad, I know!

How big is your pond? That many koi require a good amount of water. Sometimes we can do the same thing every year, but the one thing we forget that we cannot control is that the fish keep getting larger. You may have just hit a point where your fish got too big for the pond, and as @MitchM said, they ran out of oxygen when the pond was covered with ice and snow.

Even though all of our koi died, our big, ole goldfish did just fine. Smaller fish in the same pond - different requirements. We won't ever have koi in our pond again for this reason. While our system can support the koi when everything is perfect, one change can be the dipping point to disaster. We had a similar situation a few years ago when the koi were 1/4 the size and they were fine.

Post a few more details and perhaps we can offer some suggestions for a better outcome in the future.
 
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Very sorry to hear you lost your koi :( I agree with @MitchM and @Lisak1 about lack of O2 probably being the culprit. I have 4 large koi and run a Pond Breather and small aerator over the winter, suspending the sir stones about 10 inches into the water. I also have keep a back up Pond Breather and aerator in case one dies over the winter.

This is the third winter I've also covered my pond with a pool solar cover, which really helps keep the water open and minimize evaporation.
 
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Sorry to hear about your koi dying. I would be devastated. I've had some of them for 10 years.
A lot of things can go wrong. Koi get larger real quick as Lisak1 said. How many gallons is your pond, how large and how many koi do/did you have?
Something could have gone wrong with the water chemistry too. Have you tested it lately?
 
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I have an air stone and a breather. I also have a backup deicer just in case. My air stone is kept up about a foot below the surface with a string. I have a small 550 gph pump in a bucket filled with lava rock with a pvc pipe running up to just under the water surface. It creates a fountain.
There have been times when the air stone and the fountain have frozen over, but the breather was still working. The fountain looks cool. It forms an ice dome over the spewing water.
 
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This is the third winter I've also covered my pond with a pool solar cover, which really helps keep the water open and minimize evaporation.
Pool solar cover? Interesting. What zone are you in? How does that work for a pond? How does the pond "breathe" with the solar cover on its surface? Here in zone 6b, I would think the cover would just freeze to the ice and not allow gas to escape.
 
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Another point I would like to make to the OP...it's not just about getting oxygen to the fish, but the idea is also about a method for the bad gases to escape.
 
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Pool solar cover? Interesting. What zone are you in? How does that work for a pond? How does the pond "breathe" with the solar cover on its surface? Here in zone 6b, I would think the cover would just freeze to the ice and not allow gas to escape.
I have a "structure" of long boards over the pond, making a wedge shape and drape the solar cover over it...it isn't on the water's surface. @callingcolleen1 uses cattle panel frames to make hoop house type structure for her Canadian pons.
 
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I have a "structure" of long boards over the pond, making a wedge shape and drape the solar cover over it...it isn't on the water's surface. @callingcolleen1 uses cattle panel frames to make hoop house type structure for her Canadian pons.
OK, got it! Sounds good!
In the fall I use 3/4" pvc pipe bowed over the pond with netting attached to keep the leaves out. I suppose the pool solar cover could be attached in the same manner. I hammer (into the ground) fiberglass reflector driveway marker sticks and slip the pvc onto them creating the bow shape.
 

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Sorry to hear your koi died. I have been keeping my pond pumps running all winter to ensure the koi have fresh clean oxygenated water all winter, as a heater alone does not circulate water and keep it fresh. I do not have water falls but instead I have "water balls" that circulate and push surface water to ensure good circulation in front of heater. I also cover ponds with cattle pannel cold frames (but never used to for years) but with bigger upper pond that was added, the heater was not as effective, so I started covering ponds couple years ago to conserve energy.
 
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I have never heard of cattle panels. I looked them up at Tractor Supply online and those things look great! I'm going to go there and look at them in person. I'm guessing you can secure the ends to the ground creating a bow. I've been using pvc pipe, but these look like a better support for the fall leaf netting. My net would sag a little between the pvc pipes.
 
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I have never heard of cattle panels. I looked them up at Tractor Supply online and those things look great! I'm going to go there and look at them in person. I'm guessing you can secure the ends to the ground creating a bow. I've been using pvc pipe, but these look like a better support for the fall leaf netting. My net would sag a little between the pvc pipes.
Most cattle panels are metal, so would not bow, but stay flat. They can be set on something to go across the pond, cinder bricks or wooden supports around the pond would suffice, but what ever you use, make sure it’s sturdy.
 
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My large koi fish died
Most likely it was because of lack of oxygen.
Floating heaters are borderline effective, and if they were ever covered by snow and ice, even temporarily, the fish could have run out of oxygen.
It depends on a lot of factors.
I had 2 of those donut heats, as I have every winter. Last winter I left the pump running wit the water falls and the 2 donut heaters on and survived. I didn’t do that this year because the the whole falls froze solid, I live in northern NY, Rochester where we have harsh winters and thought it might ruin my pump. I also made sure and checked whenever they were covered with snow to clean them off, maybe I didn’t check enough and that was my problem. I guess the big fish needed more oxygen, I’m happy my smaller fish survived. Next year I will try and check into using the balls or the cattle fence or something else that was mentioned. My pond is about 30/35 inches deep/7-8ft wide and I have enjoyed it for about 6 years.
Any more ideas, would be very much appreciated. Thank you all very much for your advice!
 

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You say donut heaters. I'm wondering if those are the ones I use to protect my cables. If so, they are 100 watt. Not enough to keep the ice open in really cold weather. Mine iced over for 2 days but I also use pond breathers and have 1500 watt heaters as back up.
 

addy1

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Sorry about your loss. I use the pond breather, do not have koi.
The main issue in the winter is not the temp of the water, but the lack of air exchange. Rotting plants release gasses.

My 1000 gallon pond froze over solid, it as a good load of shubunkins in it. I had only a pond breather running no fish loss. When it melted this spring the bottom was covered with huge leaves that blew in from somewhere. They would be rotting over the winter. I am glad I had the breather running.
 
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You mention the pond breather...
I loss two large (24") koi this year. The only thing I did different was instead of using my 250 watt K&H floating deicer, I used my new API pond breather. IDK if that was the reason.
I still run the air stone and a bucket with a pump covered with lava rock with pvc shooting up as a fountain.
There were a couple of periods when the air stone and fountain froze over for days. The breather was the only thing that I was relying on. I'm Leary of it because it doesn't really leave a large clear hole, just that internal tube.
 
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mrsclem

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This winter was extreme for a lot of us. We were fortunate here that it wasn't bad. I haven't used my 1500 watt heaters for years but made sure they were in before the ponds froze. I have never run air stones once the weather gets cold. Pond breather in each pond, 100 watt heaters to protect cables and 1500 just in case. Every pond is different. So far I have had no winter kills and both my ponds are above ground.
 

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