Dead fish in garden pond last night

[dmf558]

I've just removed 20 dead fish from our garden pond. I've never had so many die in one go before. Mostly small Koi but four large ones as well.

I regularly clean the filters but not sure what else I need to be doing as we took over the pond when we moved into the house a few years ago.

Any pointers would be helpful.

David

[King Edward]

Given the hot weather, could be lack of oxygen. I think large individuals are generally more susceptible to this, but I don't know much about Koi keeping.

[markbugman]

Lack of oxygen is the most likely cause but have you done a full water test (ph levels,nitrite,nitrate,amonia)
regards
Mark

[tom00_uk]

worth checking the water parameters for ammonia etc, but its likely the pond was stocked beyond its capacity and the warm weather took effect.

how big was the pond as thats a lot of fish, /Koi are big messy fish and need a lot of water per fish so stocking levels in koi pools is often quite low