I have a silly suggestion. What if you taped a picture of another fish, or plant on the outside of the glass that he rams?Well he's back at it...I wonder what it could be. Should I medicate anyways? I don't know if it could be serious...
I think my yellow tang sees a reflection once the lights in the room go out, thats when he starts acting funny. But he's growing, healthy, and very yellow; so as of now, im not worried.