Looks like RTN. You can take it out and dip it in a iodine bath to see it you can stop the regression. Not normal. Is it a new frag? Sometimes new frags take a while to heal up, iodine dip should help with that too.
No was one of my first purchases. I did have a recent accident in my tank (1/4 c of pellet food dropped in). Everything seemed to survive and currently my Chems are good (just had lfs test them today)
Nitrates could be high which would cause tissue RTN. Lps love a little phosphate but not much nitrates. Do a 25% water change, making sure to use RO water and it should be fine