Ich certainly appears to come and go. However, this sounds almost too quick. The stage of ich that you can see (trophont) is supposed to be attached to the fish for ~5-7 days before falling off and multiplying. Within 2 weeks, there should be a new crop of these (with perhaps many more spots). I am wondering whether the spots may have been there longer but you didn't notice them until they got to be their largest.
Another possibility which I have noticed on my own blue tang is sand granules. When I have done a major tank disruption, the tang seems to have gotten sand into its slime coat. They usually disappear within a day and do not show up again unless I mess up things in the tank again.
I'd keep an eye on the fish before doing treatment. Do you have a QT? This is a necessity for this hobby. While you are watching, you should get this tank established (partially cycled) so you can either treat your current fish or prevent any newcomers from bringing in disease.
