Tissue loss

[jerrod]

Any idea what could cause the loss of tissue towards the bottom of this coral. I first noticed it about a month ago and it hasn't changed for the better or worse so really not an issue just curious at this point. All other corals are fine and there aren't any corals close enough for it to be stung. Could this be from shading or do you think it was a case of RTN/STN that stopped. All parameters consistent and ICP test came back with no alarms. Main ones as follows.
240 Gal display 20 gal frag 60 gallon sump/fuge
SG: 35ppt
DKH 8.5
Ca 430
Mg 1500
Nitrates 8
Phos .06
avg ph 8
Lighting 3x Orphek's Coral growth and color program

 

[TX_Punisher]

Hard to tell from the photo but I’ve seen shaded areas lose tissue in that matter.

checked for any critters munching on the base at night?