I'm also leaning towards IndyReefMan's view, the corals do look like suffering from UV burn.
Why I say so is because I used to have (or still am having albeit at a lesser degree), very similar problems with my corals. Monti can't stay alive, they look ok for a week, then bleach, the tips lose tissue, algae grow on them and eventually the whole piece is gone. Some of my acros have the tips burn issue but some are doing extremely well even though they are next to each other.
I started to have this problem after I change my ballasts and a new set of bulbs (reputable brand). My corals when into hibernation, no growth or very little growth. My Ca and kh climbed to 500+ and 16 respectively. I have to tune down my CR tremendously to bring the parameters in check. Initially I thought the corals were affected by alk burn due to the spike in alk but after returning and maintaining the parameter for almost 2 months, my montis are still dying.
Then I began to notice my hardiest and fastest growing coral, a blue stag starting to get tip burns after it grew above a certain height. The lower tips are ok, only those that grew above a certain height.
That's when I decided it is the lights that is causing the problem. I've now changed my bulbs to a different brand for 2 weeks and the corals seem a lot happier. I still have one or 2 pieces who are still suffering from the residual effect but overall, things look a lot better than previously.
I took me almost 4 months to realise this as I never thought the lights was the root of the problem. I've used the same bulbs before with no ill effect and being of a reputable brand, I thought nothing of it. It could just be a batch problem or something else.
However this goes to show, we cannot take anything for granted. Now I'll be breaking out in cold sweat when my bulbs are due for change.......