I'd say it is normal only because I noticed the same. Mine didn't rub before he went in QT. There was one week that was pretty bad with him. But he pulled through. I did water changes every 2 days or so but I had a 20g. However, there was one spike that scared me and I thought I was going to lose the tang around week 5 but he was fine with a rapid massive water change. Just stay on top of the tests daily and monitor how they are doing. If they are eating, if the spots where the cysts drop off look like they are getting infected, etc.
Oh...and prepare yourself for diatoms if you're not already seeing them. A hospital tank was depressing enough, but one with diatoms was really on my nerves at the end. Hang in and post when you get week and want to cut the fallow period short. I did and Subliminal talked me through it like the champ he is.