Chalace pulling away from base.

[gotfrogs]

I noticed that a few weeks ago that the flesh on my chalice started pulling away from the base. Thing have gotten progressively worse. Any idea what is causing this and can I save it? I grew this guy from a tiny frag and would hate to lose it. The other corals in the tanks seem normal.

Water parameters are as follows
SG 1.024
Mg 1500 (could this be the problem?)
Ca 425
Alk 9.75 dKH
Phosphate 0.9
pH 8.36
Temp 78.3