Well, this has been a not so fun morning with this tank. I woke up to most of the fish dead.
Here are my thoughts on what possibly happened. Last night I took off the overflow box and scraped off a bunch of palys that had grown in it and where blocking the intake holes. I rinsed it and put it back in the tank. It seems I didn't notice that my skimmer air intake had clogged up. Well, there must have been enough paly guts left (I though I did a good job getting them off) to dump palytoxin in the water, and that combined with a reduction in oxygen in the tank caused the die off.
I have fixed the skimmer, changed out the carbon, and am doing progressive water changes through the day.
Only fish were affected.... and not all, though most. I lost all of my oldest fish: Scopas Tang, Twinspot Bristletooth tang, Coral Beauty Angelfish, and the two Talbot Damsels (can't say I am *that* sad they are gone, the little bullies).
My fox face is breathing hard, but still alive. My new Starry Blenny seems to be OK, and has been enjoying the bully free tank this morning by swimming all around. I haven't seen my bluespotted goby that lives with the tiger pistol, but I have seen the tiger pistol excavating new tunnels now that he is not competing with the Damsels (see, they were bullies to everything!).
All the inverse seems fine, and so do the corals.
Sad day, but I guess it could have been worse.