IME, hack and slash... Remove any and all dead tissue. Dip any remaining healthy frags in an iodine based dip. My tendency is to wait too long...

as for the Monti...I can't remove it as it is actually part of the rock work now (it is firmly attached to 3 large rocks...maybe 60 pounds of LR)

I went in tonight snapped off the stag and turned it so it wasn't touching the monti....the gave it everything I had to break off either the monti or a large chunk...no go man (it's an inch and a half thick) so instead I broke off a bunch of healthy frags and apoxyed them to the rock work a little to the left of the mother colony.

Any tips on how to cut it wile still in the tank?

are you using a R/O unit?......do you know what the TDS is of the water your using for top up and water changes?

I Just changed all my pre-filters in my RO unit, membrane is about 2 years old and probably should be changed asap....unfortunately I don't have a TDS tester....but I could take a sample into the local water place to get it tested tomorrow. Our water is surface water...mid summer it is around 80-90 right out of the tap.....but I've never had it checked during spring run off.