What's wrong with my Montipora?

[Fishfreak_MA]

Hey guys. Is this brown jelly disease? My orange Montipora had been growing really well. Now all of a sudden it looks like a wound on the edge?

Parameters are
Ammonia- 0
Nitrite- 0
Nitrate- 1 or negligible below 2 on the Red Sea kit
Phosphates- Milwaukee tester on order. Red Sea doesn't give an accurate reading. API less than 0.25 but who knows what.
PH- 8.1
KH- 10
Calcium- 400

 

[Fishfreak_MA]

Forgot to mention, Salinity 1.025~

 

[Taahirs]

Any corals close to it? Looks like it got stung by another coral.