Any ideas what's going on here?

[Rabidbeast666]

My Monti has been doing fine and is growing. But in the last 2 weeks has developed this necrotic looking spot. Any ideas what could be causing this? I may have hit it with the alkalinity portion of B-ionic when dosing with a syringe but that's all I can think of. My parameters have never been better and everything else is fine.

 

[Dburr1014]

That's not a monti.
Looks like a chalice.
Did anything fall on it or did it get dropped?

 

[Rabidbeast666]

Not to my knowledge. It's at the very back of the tank and nothing really goes on back there.

 

[Cell]

favia or war coral, feed it.