Dieing SPS

[tang daddy]

From my experience, sps rtn isn't caused by pests because no animals can consume a large colony in one day. I had some sps rtn before, some were wild colonies and others was due to heat in the summer with temps rising above 89f. I also had a tank crash because of meds and disturbing the sand bed. But since you don't have wild colonies and run a chiller there's definitely something in the water. Have you been dosing anything new when you started to notice the symptoms of rtn? Something in the water that the sps don't like for them to die off so suddenly. Hope you get the problem rectified soon, I would say like others have suggested maybe some water changes to dissipate whatever is poisoning the sps.