Thanks! Best I can figure is I did a regular water change and ran out of Stresscoat that I usually use to dechlorinate the water. I grabbed a bottle of Amquel I had around from my freshwater days. Since fish are much more tolerate of chlorine than corals, I think the Amquel was outdated and did not dechlorinate the water. Within a few hours of my water change all corals were gone.
Here's a link to the thread about that if you want to read more.
Christmas Tragedy in My Tank