Montipora digi question

[Haus40]

My monti digi has been thriving until I noticed the polyps stripped off-in an area that spread over the course of a week or so. There is no predation I can see (unless my emerald crab has gone rogue, and I’ve never seen it), and no sign of bugs (and I’d think the yellow coris wrasse would be picking at least). Two possible culprits I can think of-I’d used hydrogen peroxide to treat a large algae outbreak; or the effect of me fragging the plating monti next to it, and it releasing toxins in response.
Interestingly a piece that had broken off of this digi (due to my clumsiness) has re-grown polyps in an area previously bone white and smooth, so I’m hopeful recovery is around the corner. That piece is in the foreground of the attached picture.
Some similar smooth white areas appeared on another sps (spongodes) on the opposite end of the aquarium and have also started to re-grow polyps, so I’m thinking the hydrogen peroxide did it. Hopefully they recover-and I’ll be loathe to use h2o2 again!
Has anyone experienced something similar, or have an explanation for this?

 

[Shaddow_wolf169]

I would cut that peice out looks more like rtn to me. Or take a chance on a full recovery or full loss. Me personally digi are cheap I would just leave it alone and see what happens