I stopped feeding frozen for a while once the CBB acclimated to freeze dried, it honestly seemed like my corals started to suffer (though this could be for other reasons, of course). I lost my Immortal tort, which I was very sad about. Strangely - it wasn't traditional RTN/STN, but it started with loss of PE. Then the flesh, throughout the entire coral, just started to get thinner and thinner - like it was wasting away. I tried a 6 hour cipro dip, which has saved acros in the past, but to no avail. Fragging it up didn't work either.
This is kind of what prompted my SPS flesh health post - when I lose acros it is rarely due to traditional STN/RTN. It's almost always what happens here with the immortal - a slow thinning of the flesh over many weeks. Sometimes this happens while they continue to build skeleton and branch out.
Anyway I started feeding frozen heavy again to get the longnose butterfly going (see him the pic below!) and coral color and health seem to be improving in general. I think the longnose is going to make it - successfully acclimated into a tank with a PBT, 2x yellows, purple tang, kole tang, convict tang, tomini tang, and a CBB. Just about ALL of the fish listed picked on him at some point, and still occasionally give him a swipe - but everything is generally harmonious again.
Also removal of the huge red digi is now officially on the "to do" list in my tank chore journal....