All my fish died overnight

by Cliff
(Montgomery, IL)

This is our fourth year in a 550+ gal pond. It was our most successful sping, water is crystal clear, plants and fish both thriving. We purchased two small koi yesterday and introduced them to the pond, still no problem. We woke this morning to a pond that looked like somene has dumped soap into it. A thick skim of foam and bubbles in the waterfall the size of your fist. Everyone of our fash are dead. Testing does not reveal any issues, salt was down a little.
Do you have any ideas of what could have happened

Doug says sounds like somebody dumped soap into your pond. Other than that - moving from healthy clear water to scum overnight is not something I've seen. I've seen conditions deteriorate quickly but not from great to terrible in 12 hours.