What's going on? Emerald crab, pistol shrimp, coral banded shrimp, harptail blenny only possible culprit. It had a small piece out of it then it was all of a sudden like this today. Within a small amount of time as I observe my tank through the day.
I’m not sure what the answer to your question is but I wanted to point out that you’re in the sps forum. You would probably have better luck in the lps forum since that’s what the hammer is.
Do you have any type of urchin? I had the same thing happen on a few torches, before I realized one of my urchins would do that. I believe it was unintentional, but occurred because they were eating coralline encrusted on the skeleton.
I had an emerald crab do that to one of my torches. Never went after the live tissue, but dug a hole in the skeleton. Was really irritating the torch, so I relocated him to my nano.