I posted a month ago about a similar thing. I had a black sail fin blenny that was fine for 3 months or so and I caught him eating one of my acros one day. Put that acro into my frag tank to save it. Next day he was onto another acro. removed that one, next day same thing. I was able to catch him and put him in the sump.
One acro lost so much tissue I decided to glue it. Its already encrusted about half way over the glue, and all three acros are recovering well, after a month or so.
No more blenny ever for me.