black spot on tang

Hi Guys I have a Naso (Lipstick) tang about 5 inches. Who is covered in black spot. I can not find any treatments for blackspot other than a fresh water dip. I did this for 5 mins yesterday and it made no difference if anything it looks worse. I don't really want to do this again and stress...

I noticed these 2 spots on my naso this morning they were not there last night and no other tangs or fish in my tank have them. Not sure what they are he sleeps in some rocks that dont allow alot of room could it be bruising. I am just hoping its not worms.