RTN or hopefully something else HELP

[Reefie]

My guess is going to be that the coral RTN'd due to stress from lack of light acclimation. LED's have a way higher PAR than MH's and other lighting. New additions to your DT should always be drip acclimated to match the "water" parameters, but what a lot of us (Myself included, until recently) fail to "light" acclimate and let the coral adjust to our individual lighting. It's a lot for a coral to go through to get it's arm cut off, glued to a plug, tossed in a bag of water, get driven or shipped to its new home, dumped into another tank, get blinded by a new light, and then be expected to grow.