Something eating my stick coral?

[Reef pete]

Looking for possible answers to what is eating/happening to the pictured coral. I just noticed it last night and seems to be rapidly accelerating. From what I see
the corals skin is peeling off to reveal the skeleton underneath. Recently started using coral amino and reef blizzard again about a week ago. The corals color and polyp extension were increasing that's why I'm confused about this strange issue. Thanks for the help in advance....

 

[TopShelfAquatics Verified Sponsor]

Hi there, that looks like RTN/STN. What is your water quality like? When was the last time you tested?

 

[Gareth elliott]

Any changes to your lights?, changed carbon? Never had a pest start in the middle. And alkalinity burns usually start in the tips.