I don't think it's something messing with it because I've had 2 acros in the system for a couple of months and I've only had 1 problems with corals and that was my urchin eating algae of the side of this little hammer but than he ate the entire thing
Sometimes acros can do that, just rtn overnight with no cause to be found. Hopefully it's just something with stability or water parameters that'll be easy to correct!