Tang picks on softies

[Coleus]

I currently have a hippo Tang and salfin Tang. I saw them occasionally nip on these corals. I also have a gold angel that I rarely see. My acan and brains has not open fully lately. I am wondering if it is the angel or tangs that are picking on the brains.

I do see my angel nipping on zoas and green paly sometimes

I got to admit that i have fed my tangs only once a day because of my high nitrate.

Anyone has experienced with Tangs nipping on soft coral like acan and brain corals?

Thanks