Chalice receding around edges

[MaddReefer]

Anyone know what causes a chalice, to start dying the edges ?Mag 1330 Calcium 420 alkalinity 9. How do I stop it?

 

[LPS Bum]

My first two thoughts are is it being stung or nipped by something else, and does it have a bacterial infection?

LPS corals can be tasty to fish or stung by other corals. If so, you’ll need to take action. If it has a bacterial infection, a 15-20 min dip in iodine (I use ReefDip) works well.