Rule out the basics first; what are your water parameters including alk, calcium, and magnesium? How are you maintaining those levels i.e. 2 part, kalk, calcium reactor? Whatever you're dosing with could be causing some unwanted water swings weather it be spikes in alk, Ph, or not enough of something. I know I did some harm with a huge Alk swing when I added my calc reactor in efforts to dial it in. Lost my orange setosa that week :(
I lost a lot of my reef pet corals too but it was from RTN. Sadly there isnt much information or explanations of RTN and STN so it is hit or miss but when it happens, it seems to be contagious. My reef pet acros did well for a month until I added the corals from mr. coral. Those corals showed signs of RTN and it spread like fire which is something a lot of hobbyist that experience it have noticed. I removed the remaining sps frags that suffered from it; salvaged whatever corals I could with a healthy frag clipping and tossed out the rest which pretty much solved the issue. Unfortunately I lost a lot of corals before solving the problem. As for your lighting, youre fine. Infact, you could probably bump it up to 50 or 60%. Remember, youre trying to mimic the sun in your aquarium so in a sense, you can never have enough lighting however you do want to acclimate any coral to your lighting spectrum. I started my sps frags on the bottom sandbed for roughly a week, then moved them halfway up the next. Within a months time, they were mounted throughout the tank all over the place and my lighting is pretty intense with par ratings equivalent to a 400watt MH as I'm running 60 degree optics and over driving my LEDs. Not to say that the lighting isnt your culprit but I would look more into your water parameters first. I'm sorry for your loss, I know how expensive it is and can be as these colorful frags aren't cheap but I guess its a part of the game of keeping ocean creatures in glass boxes.