I doubt that the feed is the problem. Like TJ, I don't use Purina but have often used it with no problem.

The problem will almost certainly be environmental and the runoff from fields is a wild card. Fish that are feed trained that don't come to feed are unusual in a healthy pond. BTW, in a fish kill, 95% of the fish don't float.

I would have a complete water test done. Aquarium stores can probably do this.

No idea whether the mixing of water from aeration could be a problem.

At this point, I can only offer condolences.

It's not about the fish. It's about the pond. Take care of the pond and the fish will be fine. PB subscriber since before it was in color.

Without a sense of urgency, Nothing ever gets done.

Boy, if I say "sic em", you'd better look for something to bite. Sam Shelley Rancher and Farmer Muleshoe Texas 1892-1985 RIP Grandpa