dead spot on BN

[tibob32]

My blue polyp birdnest has had a dead spot for a while. The spot is not growing nor shrinking. Is it because bird nest don't tend to encrust back over their dead parts? The remainder of the coral is very healthy and growing fast

p 8.1-8.3
temps 78-80
dkh 8.5
cal 450
mg unk
amm/phot undectecable
sg 1.026