Stn?

[reefermadness]

From your description I would say it was RTN from the start.

STN happens over days/weeks and usually is quite slow working from the base of the coral. Usually STN does not kill the coral but if stress continues then it can turn into RTN.

RTN in comparison can happen in a matter of hours to maybe a couple of days if the coral is just hanging on. The corals starts peeling/flaking flesh off and the coral is usually unsavable.