just got back from Mexico and did some snorkeling....observed tangs there and a good majority of them rub on something most of the time. Also the more I read about tangs, they do this a lot. My regal does the same thing. I had him in QT
for 6-8 weeks and 4-5 of those weeks in Cupramine. he developed HLLE
and his poor face is begining to heal nicely. Has been in my main tank for about 6-8 weeks now. he rubs his face against the substrate and rocks from time to time and assume its because its healing. My point is they can rub for no reason at all or because they simply need to!! Just watch for white spots...otherwise he is just rubbing!!