Chemistry or worm of some sort

[quickgranite]

Can't figure out if this was a ca problem, precipitation for far to long or some kind of worm eating the coral. Heads look great eats at night. Coral makes me scared. Didn't notice until I was working on a clean up. In the photo the left branch is holding on by a thread

 

[taricha]

These corals, the tissue retreats from the old skeleton, other things move in and make it home. That's not a dissolving skeleton chemistry issue.
No big deal, it's a frag. Or break it off and super glue back to the colony if you want to keep it all together.

 

[quickgranite]

starting on the other side. Any prevention? Should I dip it?