I had all my tests double and triple checked by the lfs and I even bought a few new ones for myself, all the tests were coming up consistently normal. I always keep my alk at 8. My nitrates were at 15 and still are, even with things looking much better now. I didn't leave all the dead corals in there, some were absolutely gone with no signs of tissue left. A couple that had a slight amount of tissue were left in there and are starting to come back. There could be something else going on beyond just the salt change, but i'm pretty certain not with anything I can test for. I am changing a little more water now, but my tank was looking great for a long time on my old schedule and things just started slowly degrading. I wish I had a solid concrete explanation, but at least it is headed in the right direction now.