Hey MR, recently my frogspawn and hammer coral even candy cane coral keep dropping their heads time by time! Water premeter was good,others coral was good,just dkw. Please lmk if any of reefer here knows why and how to fix it. Tanks in advanced!
In my experience, this happens when the phosphate levels were too high, chonically, and after a few months, they pop out intact. The tissue completely detaches. At this point there is not much to do, even if you were to do a complete water change with zero nutrients, the tissue will not reattach. Some people have held down the heads with mesh, until new skeleton is grown. This is assuming that there is no other tissue rot or biological predation/warfare going on.