The fog/oxygen thing doesn't make sense to me either, EdT..but it's what they were told. The other fish were fine, only cats died.

We are having big temp variation this winter.
Fog wouldn't have risen if the water wasn't warmish, and fish don't have a lot of options for relocating when they live in a pond.

It sounds made-up to me, but it IS what the cons dept told them.
I guess I don't know enough about it to have posted, but I thought it went along with the thread title.