All my Large Koi died over winter, Why?

[mrsclem]

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]

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.

 

[poconojoe]

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.

 

[Tula]

I use a Pond Breather too. Why did your air stones freeze ?

 

[mrsclem]

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.

 

[poconojoe]

I use a Pond Breather too. Why did your air stones freeze ?

If it gets cold enough, water will freeze above the stone. The bubbles are still running under there, but ice closes the opening. The stone is 12" below the surface.
The fountain only rises about 8"-10" above the surface, when it's real cold an ice dome forms over it.

 

[mgmine]

Carmine we're almost neighbors, probably 20 miles apart. As for the 13 fish, how big is your pond? To me, that's a lot of fish and if one was sick (you added new ones in the fall) this could have been the problem. Overcrowding, a sick fish and no water changes sounds like a breeding ground for something bad. Add to that the decaying fish floating in the water for 5 months and nothing survived. I would drain the pond and start fresh.

 

[Tula]

If it gets cold enough, water will freeze above the stone. The bubbles are still running under there, but ice closes the opening. The stone is 12" below the surface.
The fountain only rises about 8"-10" above the surface, when it's real cold an ice dome forms over it.

Gotcha ! I cover the pond for winter, so in my case I don't face the same issue.

 

[CometKeith]

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.

I'm very sorry about your fish. My setup is similar to what other people have mentioned. I did not lose any fish despite temps going below -25 F this winter. I run a water pump all winter long. When the piping is covered with snow the water still recirculates under the ice and snow. I also run an airstone and a pond breather. Even when we had a foot of snow on the pond and below zero temperatures the fish were still okay. I have never used a pond heater or covering but my pond is 4 ft deep so the fish are able to go to the bottom where it's warmer. The largest fish need the most amount of dissolved O2 so when something happens to the largest fish and not the smaller ones it's a clear sign of inadequate O2.

 

[Lisak1]

@callingcolleen1 has a setup that has been successful for her for many, many years so I won't argue with her conclusions. However, I will tell you, here in Chicago I have visited lots and lots of ponds that are only 24 inches deep. The fish - and most are big koi - stay in the ponds all winter long and they do fine. I think it's important to keep the pond running all winter (which requires some forethought in the design of the pond) and keep your fish load low. Conditions like overcrowding that are hard on fish in the warmer months are made more difficult in the colder months.

And I agree with Colleen that the ice does displace water, but in my experience the ice only gets so thick. So mild winter or really rough winter - the ice cover is basically the same. We experienced the famous polar vortex this year, but the ice was no thicker than it has been in some of our milder winters. Snow cover helps, so we always welcome a nice blanket of snow on the pond, but that's not one you have any control over !

 

[steeledeal]

Poor koi. The winter season was really harsh.

 

[SEKCOBRA]

Sorry to here about all the losses this winter. My pond froze solid then thawed multiple times this winter. Second winter with the pond and I left pump running to the falls and the aerator running again. I do move the aerator up and place it on a rock a foot below the surface. I have about 20 Koi and some bullfrogs that all survived thankfully. My fish are still pretty small. Most about 6-10 inches. I'm thinking I will have to thin the herd when they start getting big. I'm pretty conservative with food. I'm in no rush to grow them. This time of year when the water is still on the cold side makes me more nervous then the winter. Last year parasites attacked my fish during the spring. I'm keeping a close eye this year and so far so good.

 

[Learning to Care for Koi]

I also lost a large koi over winter. A couple small fish remain but, to be honest, I bought them in Walmart as Butterfly Koi and I am wondering if they really are. Anyway, I think it must’ve been the oxygen issue.
We kept an aerator running and always had a hole in the ice at least a few inches wide – I imagine the exchange of air and oxygen must have been insufficient.
Would wintering the koi over in an indoor aquarium be an option?
Is there a similarly beautiful fish that I might use in my pond in the summer and release into the St. Lawrence River in the fall?

 

[Norfolkpond]

@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.

Very helpful ! Thank you!