vmalpi said:
Long Tentacle Anemone
It looks like you have a tan LTA near the front of your tank.
LTAs have a sting that can kill some corals.
My LTA got wanderlust and went on a long walkabout and when I came home he had accidentally stung almost every coral in the tank and a featherduster.
The smooth skinned mushrooms didn't seem bothered by the sting.
The candycane turned white and lost some flesh in small spots where it was stung.
The red rhodactus mushrooms shriveled up and expelled all their intestines like a birdsnest of white thread.
Same for a brown fuzzy mushroom.
A bunch of zoas and button polyps stayed closed for days afterwards.
The featherduster's gills all shriveled into little curls before he "popped his crown".
I moved all of the corals into a different tank and they all recovered fully.
The featherduster has been in there a long time and is attached to several large pieces of LR so I don't know if I can move him or the rocks without killing him.
So far he's been recovering also and his crown is about halfway grown back.
Hopefully I'll figure out a way to safely move him too before my LTA decides it's time for a new "view".
That's just my experience, and I really don't know squat, so take it for what it's worth...