No major recent changes in parameters (8.5 alk, 430 Ca, 1300 Mg, 2 ppm NO3, 0.06 P, 8.2 pH, 34 ppt, 79F) or livestock (1-2 emerald crab, clown, six line wrasse, royal gramma). The ducan tissue doesn't appear brown, but heads are closed.
Mine started going looked the same after neglect/ alkalinity swings. I dipped mine in iodine and it stopped deteriorating. Lost 3 heads dipped it when 2.5 were gone.
I would do either the seachem dip or iodine and watch/wait
For iodine solution, mix with tank water to form a light tea color solution, dip for 10 minutes.
When you get the SC reefdip, follow the instructions and give it a second dip a day later. If you see improvement, dip it again a day later.