Dead Koi

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Very strange but I lost about 20 koi in my pond during the winter months. When the water was cold they never really went to the bottom and sort of hung out under a cave near the surface. All water parameters were good and the pond is close to 4,000 gallons and almost 4’ deep. I installed a heater and airstone near the surface and kept my falls running.
Could it be that I bought cheaper koi and one got sick? I also lost one from a reputable dealer who only buys from Japan directly. I have one that is actually seeking refuge in the skimmer box and when I take him out he is back in there in a day or two.
Any guidance is appreciated
 

Mmathis

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So sorry! That’s devastating!

What were the actual numbers from your water tests? Numbers give more information than “all parameters were good.” What kind of filtration do you have?

If you lost 20 koi, how many did you start out with, and how big are they? Yes, they could have been sick.

EDIT: In a previous post, you estimated your pond at around 3300 gallons.
 
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Oh no! I feel your pain - this happened to me one winter, but in my case it was a pump failure that couldn't be managed in the dead of winter. But losing that many fish is sad.

When you say "during the winter months" you mean now, right? Here in the midwest we are still in the thick of winter... I would have no way of knowing what's going on under all the ice and snow. Is it not the same where you are?

In addition to the questions @Mmathis asked, I'll add one more - you mentioned adding new fish... when did you add new fish to the pond and how many did you add? How many did you have previously? Are the new fish the ones that are dying?

Again - so sorry this has happened. Stick with us and we will try to help you figure it out. Sometimes we do things that inadvertently cause fish to die; other times it's outside of our control.
 
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It matters not if it is one of the highly respected dealers or not They are not immune to disease though they will make great strides to avoid any . All it takes in one person to have there hands in there pond and go to the store stick the hand in there water and you could have issues. Pond to pond ever see a duck at your pond? they could have just brought you unwelcome gifts
 
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I'm interested in your responses.
Too many questions...

What was the weather like when you added the new fish? I hope it wasn't Winter.

How many of those 20 fish are new to the pond?

How many total koi are (or were) in your pond?
How large are your koi?
Maybe there's just too many and not enough oxygen to support them.

Was the water too cold for them when you introduced them?

Did you quarantine them before releasing them?

Were there any physical signs on the deceased fish to give any clues?

What are your Ph readings?

Do you have adequate O2 infusion?

Did the pond ice over? If so, do you keep a hole in the ice for gas exchange?

Here to help, but need more details...
 
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Sorry for the delayed response. All the koi were in the pond since end of June. The only thing I can think of is I left the copper unit on to kill algae and maybe it poisoned them all. Who knows what happened actually but the pond never iced over as it has a heater on it and two air stones. Thanks for all the help and concern.
 
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Copper in concentration is used to kill bacteria and algae keep the levels high enough long enough and yes id say that could kill
 
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That’s really the only thing that could of happened. They were fine up to that point. Anyone know a good online place to buy new ones?
Thank you again
 
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All depends on your purse and quality of fish you desire.
Next day koi has some beautiful fish without huge numbers.
If you were close by I'd give you a few I still have about twelve I need to home.
 

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