Leptastrea Coral Dying?

[Aquat]

I recently bought this coral from a local hobbyist and all seem well till today after I returned from work. The upper half seem to be missing and the lower half is opened? My best guess that it got stung, but the only coral next it is an Orange Leptastrea and they're at-least 2 inches apart. Just to be safe, I've isolated it to its own corner. Could use some input

Parameters:
Salinity: 1.024
Ammonia: 0
Nitrate: 10>
Nitrite: 0
Alk: 8
Calcium: 470
Phosphate: 0.25>
Magnesium: NA

Fully opened;
http://s98.photobucket.com/user/aquat1/media/GreenLep2_zps622175d1.jpg.html

Present State;
http://s98.photobucket.com/user/aquat1/media/IMG_1523_zpsf5c4f8c3.jpg.html