From my own past experience, I learned a couple of things
1. Try not to overdue trace minerals and suppliments
2. Make sure your R/O water TDS is low
3. Make sure there is no possible contaminant getting into the tank. I once killed off an entire reef aquarium because my syphon for doing water changes was laced with an oil contaminant
4. Salt mixtures for large water changes need to be airated/buffered properly
its werd you mentioned TDS, I checked mine and it was 168ppm, OMG I checked it four times, Tap water is at 140ppm. My filters I changed in july. I have all new filters for my RODI coming today so guess what I will be doing. Pulling out my water change over tank, cleaning it out, changing all my filters and making some new ESV salt water. Sunday I will do a 55 g change. Yep all these things make SPS not happy. But glad Im getting to the problems becuase Sunday I will be at the swap with my grocery cart