Stylocoeniella issue

[DVal]

Came home to find this spot on my Burning Banana stylocoeniella this afternoon. It looks like I can see white skeletal tissue. I have 4 tangs and clownfish, so I don't think a fish did this. Any ideas? Something I should worry about?

Parameters:
Alk 8.7
Nitrate 6
Phos .08
Calcium 450
Mag 1410
1.025
78.5degrees.

 

[GillMeister]

Could be STN. Keep an eye on it. It might need to be moved to a shaded area until it recovers. I found these guys get burnt easily if not acclimated slowly.

 

[DVal]

Thank you. It was in about 150par. I just moved it to the shade.