What are these marks on my tang?

I had to par boil the broccoli to get them to touch it. (heard you can also freeze to soften it for them)
My hippo tang does get white spots when stressed but they disappeared in a day or 2.

Also try banana slices. When ever I have an old banana that is a little past prime I cut up a few pieced for the tangs. At first they avoided it like the plague and it sat there for what seemed to be 10 minutes. My adventurous Yellow Tang went over and took a piece. It was all over quick because when she when back all the fish wanted a piece.

 

Wow I never heard of giving them Bananas.