definition of rtn and stn?

[CoralBeauties]

I have an acro that recently started loosing tissue at it's base and have read on reef central of rtn and stn.   I was wondering really what the diffinition of each is and what is believed to cause each.  I ended up having to cut the main piece of coral off it's mount.  The main piece has stopped loosing its tissue but the base which was encrusted over has lost every bit of tissue.  the odd thing is none of my other corals have showed any problems at all.
jeff

[verper]

Both are generic terms for the symptoms,  not what could be the many, many causes of tissue loss. 

RTN - Rapid Tissue Necrosis

STN - Slow Tissue Necrosis