Sorry about the continued problems. One thing that has always worked for me is water changes. It might not be practical for larger tanks...but it works.
I dont have the time at the moment to catch up on your thread but I'll suggest this:
1. Stop all the dosing (other than for Ca/alk and Mg).
2. Carry out 20% water changes every 3 days for at least 10 times. Ensure RODI is working well and no chloramines are getting through. Use different salt brand (to eliminate potential issue of bad salt batch etc, or other issue).
3. Feed fish moderately.
4. Set skimmer to skim wet (need to collect 1/4 cup of skimmer cup every day).
5. Run some GAC but not so much that water is stripped.
6. Keep up the flow.
I make the above suggestion based on this: I've made plenty of dumb mistakes/followed certain trends/dosed "magic" potions. On so many of those occasions I had corals begin to strip, show signs of distress/tissue thinning, tissue looking dry.
Yet I still have many of my corals which are over 5 years old or more (my Red Planet is around 7 years old).
In all of those times of my stupidity I managed to turn bad situations around by following a protocol similar to what I outlined above.
I really hope things turn around.
Good luck.