Vigilance is the key, Quarantine the Monti's as you already have. I had them pretty bad, not in my display
but in my frag tank where I had quite a few recently purchased frags and a few larger pieces use as
frag stock.
Here is how I beat them, I used a bare bottom tank with nothing but a frag rack it. You have to check
the corals every day I sometimes checked them twice a day. Then I dipped them every other day in a
solution of salt water and PraziPro. I used about 1/4 teaspoon to a gallon of water so I didn't leave them
in the dip to long because that is a pretty strong solution,
I also scrubbed the bottoms of the corals and the frag plugs with a tooth brush. I also shook the
frags pretty vigorously in the water to shake off any Nudis that might have been under the edges of
the frag by the plug.
I had a total of 18 different frags and a few larger pieces that I had to do this with, lost most of about
4 of the larger pieces but saved almost all of the frags and a few small frags of the larger pieces.
You have to keep the tank that had the Nudis in it free of food for about 3 or 4 months to insure that
there are none in the tank so it doesn't start the cycle all over. I also have heard the Six line Wrasses
will clean a tank of them in few days but just never could find one that ate even one.
Now there is no guarantee that this will work for you also but it did for me so I really do not see why
it would not work for you. Good luck hope you beat the little Ba$tards.