Monti cap dead tussue spot

[Jake_the_reefer]

I have noticed this growing white spot on my monti cap. It goes through all the way to the bottom side.
Alk is 7.8
cal 430
Temp 78
Nitrate not sure will test soon
Phos will test soon
I have yet to take par readings as well in this system

I have inspected for pests and also did a 15 min dip in revive to prevent bacterial issues. This monti was out of a previous tank where an alk crystal fell on it causing a small burn. There was algae on the dead spot. The algae is now gone in the new system and the spot is now growing. Tank is fully cycled and was established with live rock from the old system
If i left any info out I can provide when asked

 

[Jake_the_reefer]

I will add also this is the only monti/sps with tissue dieoff

 

[Jake_the_reefer]

Any ideas?