What kind of coral is this and why am I losing tissue

[VCreamer87]

I got this coral about a month ago maybe a little longer at my lfs and they didn’t know what it was I had placed it at the top of the tank then I noticed the small dead spot in the front so I moved it lower towards the side of the rock work and now 2 days later the back is losing tissues is it saveable or a goner? Any help is appreciated thank you.
Vince

 

[Arego]

Looks alot like goniopora, perhaps a poritie of some kind? reasons why it's recessing? Endless. How about some background on your tank and specifically how long it has been stable at those levels.

 

[VCreamer87]

Tank has been up and running for about 4 months with coral frags in it about 6 months total with fish in it alk is 9.3 mag is 1375 and cal is 480

 

[vetteguy53081]

Pics a little fuzzy. Looks lie alveopora but could be cyphastrea also. Location for either is important - lower half of tank but not on sand under moderate light and water flow.
Salinity 1.025
Assure phos and nitrate not elevated
calcium 400-450

Cyphatrea: