Pond Boss Forums INTRO Questions & Observations Why HSB fish kill??

Sores are most likely due to stressors. Like was said above, C&R, etc., when O2 levels are lowest.

If that's not the case, then a couple of questions.

You said you had an aeration system. Was it spec'd out for your pond or was it one that was purchased or a put together DIY system? If it was spec'd. out, did anything change in the pond from time it was installed to the fishkill?

What was the water clarity when it happened? If the clarity was less than 24"-36" what was it due to? Clay or an algae bloom?

Large HSB are more intolerant of low O2 levels than the other fish in the pond. Boiling it down, it might be that there is too much biomass in the pond for the conditions.

You say 1 ac. How many pounds of fish do you think are in there?