Question
I have a 8x18x3 Koi pond with a pump and stream filtered at the stream,which I have had for many years last year I decided to clear up the water and used house water the same time the county clorinated the water and I lost all of the fish (some koi were 25 years old )
I have  emptied the pond and added new fish and recently read that when I winterize I should turn off the pump because the flow of cold water may kill the Koi. Should I at least have a fountain for air supply ? I live in southern North Carolina 28462

Answer
Hi Patrick,

Sorry to hear your koi have died due to the chlorine.
In my country (Belgium) high chlorine level to clean the pipes is always mentioned before it happens. So more safe!
Concerning your question, would not turn of the filter completely as then all filter bacteria would die.
Maybe reducing the flow and covering the filter and water outlet back to the pond can be covered?
This will Ensure, if the pond freezes over, there is gap due to the return flow .
This will Ensure bad gas can be removed from the pond and no pipes will crack due to cold.
Hope my answer is clear and helps out.

Good luck!
Kind regards,
Raf