I had a similar experience to shreds. A 4 year old tank that I finally had down so I could actually grow some acros that was looking pretty good. My confidence put me into a lazy groove. I noticed some stuff was looking pretty ticked off, so a big water change was performed. Two days later it looked worse, another big water change. I had tissue loss and even the lps was wasting away. I finally got out the test kits to see what was happening. Turns out my fancy 3 part salt must've got frozen in transit or something. The liquid component "A" had precipitated to crystals in the bottom of the jug. I test every gallon of water that I mix since 2017. Cal, alk, & mag. Lost all sps, the acans and zoas came back around eventually. Took awhile before I even wanted to do anything with the tank because it was my fault, not anybody else's.