Your comment was very beautiful and lovely. thanks alot my friend.I'm just mentioning this because I've had it happen in every tank I've had sps in. Sometimes a piece will RTN or STN with no explanation that I can find. If this is your first acro then by all means try to figure it out and list your parameters as folks have requested.
I've woke up in the morning to a white stick from RTN on a coral that looked good the night before. Every other coral in the tank is fine. This has probably been the most frustrating part of keeping acros for me. I'm a newb with only 18 months experience tho.
EDIT : the rock looks like this may be a younger tank? I definatly had more losses the first year. The older my tanks become the easier it gets to keep things alive that I couldn't keep early on. I attribute it to the tank maturity thing many new reefers don't like to hear.