My irresponsible livestock additions with no dips or quarantine has come back to bite me in the You better mean it as in 'donkey'.
I am pretty certain I have a case of Montipora eating nudibranchs, and the only solution is quarantine and constant dipping, and keeping your fingers crossed that something survives. I have yet to see them, but I am on the hunt as soon as the lights are out.
Top View:

Side View:

Bill's F-ing Sweet Purple Montipora with Green Polyps...getting ravaged:

I have maybe seven or eight different Montis in my 30g, and only three seem affected thus far - Idaho Grape, the purple one from Bill, and the setosa? from Jake - but the nudis need only stray a couple inches to find more. There is a digitata frag that is showing recession from the bottom up in a clean line, which could be nudis, or it could just be dying.
Looks like Bill's old frag tank is becoming my Montipora quarantine for a couple months as soon as Jake and I install this 125g. I need to get under my garbage house tomorrow and shore up the joists so it doesn't drop through the damn floor.