PDD, I would doubt that your hammer has RTN, rapid tissue necrosis as this mainly happens in sps corals. Acropora, montipora, stylopora and I've heard pocillopora seem to be the main corals RTN affects. What is going on with your hammer I don't know as I keep sps corals, but I just would doubt it is RTN. The symptoms for RTN are tissue peeling off the skeletal remains, and in as little time as 30 minutes it can take a whole colony.
Thanks for the response. You confirmed what I was wondering - wasn't sure if it was exclusive to SPS's or not. From what I have researched about RTN, I guess I should be glad - but what a bummer about my hammer. I hate not knowing a cause and how to fix or more importantly how to avoid in the future.
Is it possible that my hammer has gotten RTN? Can they get RTN? On Friday my hammer "looked" fine, I went away for Saturday, came home Sunday and one "mouth" is gone. Not good.