My research showed that unless you completely eliminate the Monti's from your tank you're likely stuck with them forever. Treating the individual colonies will knock back the Nudis, but not their eggs...in other words they'll be back.
Much like Aiptasia, the only effective method I've found is natural predation. Suprisingly Blue Leg Hermits will eat the Nudis. So will Coris Wrasses, Six-Line Wrasses, Twin-Spot Hogfish (the best I think), and Radiant Wrasses.
I had mine under control, but just had eggs hatch and almost wipe out a very large cap. I just got two Twin-spots and some more blue-legs....put the blue-legs right on the monti and the twinspots have been hunting all over it for the last few days...the destruction seems to have stopped so I think the coral is saved.
So that puts my "control team" in my 150g at:
Already Had-
1 Yellow Coris
1 Six-Line
30 or so Hermits
Just added (and halted the destruction)
1 Red Coris
2 Twin-spot Hogfish
20 Hermits
I plan on adding a six-line and a yellow coris to my Frag tank too, as well as another twin-spot and yellow coris to the main tank, maybe a Radiant Wrass too.
I feel your pain.