Is this RTN/STN?

[aaron186]

I just purchased some new frags. The stylophora was healthy when I purchased 2 days ago. I dipped with poly labs primer per bottle instructions. Yesterday I noticed a small white spot on the base of the stylo. This morning it’s grown quite a bit. The top of the frag looks healthy. I didn’t notice anything eating it. Should I do something or just let it be and hope it recovers?

 

[Timfish]

Leave it alone and be patient. There's multiple causes for tissue loss in corals, stress being a major one. Make sure pH, alkalinity, calcium and magnesium are acceptable. If possible, match the lighting it was grown under.