Don't concern yourself with the RTN/STN terminology, the term doesn't even exist outside the hobby and there is no exact time to distinguish between the two (they're both relative terms). Tissue necrosis is more of a dis-ease than a disease, caused by an upset in the tissue function due to changes in any of the external factors that corals depend on to survive. RTN is not caused by any specific bacteria or parasite, although an attack by such an organism could certainly trigger tissue deterioration, either fast or slow depending on the sensitivity of the coral. RTN is most apparent in Acro and Pocci corals because of this. You need to consider that you picked these frags up in Lethbridge, drove 2 hours to get home (did the temp change significantly in this time?), you acclimated the frags (how exactly did you acclimate?). If your water parameters were drastically different than the frag tank (especially Nitrate levels) it could very well shock a sensitive coral. Did you place the frags in too much flow or not enough flow? Did you place them too close to the light? Something as simple a soap residue from washing your hands and touching a coral is enough to kill it. Why don't you post your parameters AND a list of the frags you bought. You said 80% were affected, were they mostly SPS? You had mentioned a Devil's Hand deteriorating, soft coral are pretty resilient, if you have a dieing leather coral I would really take a look at tank conditions and parameters. My point is there are a lot of factors to consider, you probably should retrace your steps and you may think of something you might have done to trigger this.
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