Not scratching or "flashing" does not mean the tang is not infected, just that the parasites are not that much of a bother at this point if
that's the problem.
Originally Posted by souk
Wednesday morning I looked and there was no more black spots on the tang.
Since the spots have gone, a sure sign would definately be that they come back. Once the turbellarians leave the host they multiply in the sustrate and then erupt releasing the newly hatched worms into the water column to look for a new fish host. You will most likely see something by the weekend if so. If this does happen your other fish are likley to be affected as well, so keep a careful watch.