I have had my pond for 8 years and have never had any problems until a hail storm a few days ago. I went out and found them all dead. I then googled it and think it was due to the change of temperature and then it depleted their oxygen. Does anyone know or have a cover that would work for hail?

  • 1
    where do you live? In terms of climate
    – user6796
    Jul 30, 2018 at 20:24
  • Cold water holds more oxygen then warm water. How deep is your pond? It takes a LOT of energy to change water temp significantly, particularly if it is deep. Jul 30, 2018 at 21:20
  • Same deal here, year 6 in this house and we have lost koi over time probably for various reasons (probably not as dedicated pond care taker as I should be) but last night large hail (up to a 1.75 inches said the weather alerts) 3 hours without power and my koi pond was a ghost town when I got home from work.
    – Eric
    Aug 7, 2019 at 21:57

1 Answer 1


I have a pond with koi. We have had two hail storms (in ten years) that required replacement of our roof shingles twice which the insurance adjuster authorized; so serious hail. No problem with koi or the tropicals (mollies, danios, etc.)

I have inadvertently killed koi by covering most of the pond, slowing oxygen exchange. Hail hitting the pond would increase dissolved oxygen content by agitation and cooling the water. I strongly recommend using no cover. I also doubt it was temperature change, as my tropicals would be much more sensitive to cold than koi. The only thing I can think of is a very fast temperature change and that is hard to accept.

What about a lightning strike on the pond (grasping at straws)?


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