It is rotting away. I would take it out and cut off the dead tissue. Do a dip in lugol's solution(iodide). The causes are endless. What are your parameters/lighting?
PH is normal. Alk is 3.5. I know thats a little low. My cal. was low too 300. Dripping kalk for that. Sal. is at 1.024 Temp around 80 Also had good water flow on it. I don't have that to dip it in. What else could i use. How about Seachem Reef iodide?
Hopefully dripping kalk perks it up, I can usually tell when my alk has fallen because my leathers start to get unhappy looking actually. If you see any of those rotten areas progressing through the coral, they will need to be cut away, preferably with the coral out of the tank.
I don't know anything about dips for that (never had to do it).
Ya i thought it was going to make it yesterday, but today was another story. I took it out of the tank. there wasn't really much left of it. Don't understand, :? everything else in the tank is doing great. maybe i put it in the tank to quick. I let it sit in the tank in the bag, and put a little water in at a time. Did this for about an hour. I don't think my parameters are that far off.