After going back and looking at your images I would expect that you have a lot of waste build up within and under the rock wall. For now, massive water changes with aged reef chrystals and try adding some bacrteria culture. Long term, either add some more bio suface in a remote sump to deal with the waste build up in the main tank or redo your set up to eliminte the dead zones in the main display. Good luck but dont waste your time and money chasing ghosts. There is no one shot fix to your problem. Its not salt, lights, amino acids or any of that other stuff. All corals need is good water to survive. healthy corals seldom seccumb to bad light. (I personally kept a frag in my sump under a 12 watt led for 6 months just to prove that to my friends) For long term sucess you must set up a system to deal with the wastes in a manner that keeps them moving through the n cycle. The way your system sits now there is a bottle neck, probably phosphates, that is causing stress to your coral. Address the system so that the n cycle can run to the complete reduction of the waste products. After you do that and provide your corals with clean water to start with they will thrive. It isnt as hard as a lot of people on these forums make it out to be.