Help dying button scoly!

[thatindonesianreefer]

Hi
Ive had this piece for about 3 months know and it has been doing well until around a week ago when it strated showing its skeleton and a small chunk of it has no tissue but still fresh skeleton.
Some help would be nice

 

[thatindonesianreefer]

Parameters :
Ca 480ppm (really high at the moment)
Kh 10 dkh
Mg 1400ppm
Nitrate and phos havent bought test kit yet but phos 0.25 ppm and nitrate 5 ppm 3 weeks ago.(checked at store)