Thx for the replies, all.
The Monti has been in system for about 2 months. Picked it up unnamed from a LFS. It is kind of like an inverse Super Man... Red with Blue Polyps, but the red in growth areas is more of a dark, vibrant pink.
There was a small bare spot that appeared about two weeks ago, that has now changed to the apparent growing white (I'm assuming skeleton)
Yes, I noticed the growing white around the same time that the PO3 dropped.
I lowered it by adding a bag with PhosGuard to the sump, dosed per manufacturer's recommendation. The drop occurred over 4 days, which is awfully fast.
The other corals seem super happy about it and I'm getting MUCH better PE... except where the polyps are receding...
Struggling to get NO3 up. Even sucked out some of the skimmate and returned it to sump today. Result was actually a LOWER reading tonight. Go figure... lol. I'm going to turn off refugium lights every other night. Had already backed it down along with the skimmer to 4 hrs/night