although alk might check out now at an acceptable range... that's not really the issue. Even an Alk of about 6 dKH is not going to cause that massive amount of die off.
FWIW red bugs didn't help... but that's not your main issue there. I've seen corals live and grow forever with red bugs... and although they don't look their best while infested with red bugs... it still should not kill them.
Many people test their alk and think it's "ok" because the number corresponds with an acceptable range... but that's not the issue with alk... corals are tolerant of a fairly wide range of alk (as low as 5.5ish and as high as 13ish IMO) but the issue is the alk SWINGS. An alk of 3.5 meq/L (or 10ish dKH) is fine for corals... but it's not fine if it was 7 the day before... or for that matter it was 13 the day before.
Stability in all major water parameters is very important in keeping SPS. My bet by looking at those pictures is that it was a bad Alk, calcium, salinity, or even temp swing. Out of those 4 i would label alk as the most likely, and temp/calcium being the least likely (temperature people usually notice, and calcium depletion usually leads to mushy tips, not bleached/dead tips.)
So all that said, my money is on Alk. Make your Alk levels stay rock solid (consistent) and get rid of the red bugs and my bet is your issues will disappear.
