I didn’t know about the phosphates in the rock until after everything was in the tank. I wouldn’t been a better idea to use lanthanum honestly with the bleach but I had no idea.I expect your "new" salt water will be high in Mg and the other parameters will also be similar to what is in your salt mix. I think one of the Red Sea salts mixes high/similar to what you are getting?
Having elevated salt mixes makes it difficult to get dosing for CA/Alk in line because those parameters get bumped up everytime you do a water change, making stability more challenging to achieve.
You have learned, Chlorine bleach doesn't strip phosphate, only organics from old rock. I like to use salt water and lanthanum chloride in a bucket for old rock, and mabe a little bleach if the rock is totally filthy and I am in a hurry. Usually just old salt water and LC, no light and a circulation pump for me.
I don't know what is killing your LPS. Maybe start a new thread with that title and some pictures of the corals. The sickness / deaths may not be related to parameters and the water changes may have sped up their demise?
If you have brown Jelly, a picture of the sick corals would help with a diagnosis. Do you see anything on them?
The torches are brown jellying just resection of the flesh band so far, the 2 that died few weeks ago might have brown jellied or maybe something else