The free experiments should be the ones tried first ie; changes in salinity, magnesium, alkalinity, and calcium in that order. But also double check those measurements with a second test kit or recalibration of equipment. I've probably had worse luck than most with test kits and equipment being Defective (2 magnesium test kit, 3 alkalinity test kits, 3 nitrate test kits, and a refractometer being off from the manufacturer). It's difficult to trust these things when I've had so many in the past 2years. That's why I keep seconds around to verify the first when things seem off.
I know my previous posts sound like I hate on leds but that's really not the case, but I have learned with my limited success with them that other light sources are set and forget(still need to acclimate corals).
If your salt mix has that high of magnesium I strongly suggest trying a different salt. Most reef aquariums don't use that much magnesium and if your test kit is telling you otherwise I would also suggest confirming this with another test kit, just to be sure.
Where did you get the acros that bleached or STNd? From the swap recently?
