Herbtana is a fairly new product, I have some experience with it, I'm not incredibly impressed with it. It is a very weak medication. It may help with very small outbreaks, but doesn't seem to do much otherwise.
IMO, I would still remove the fish and keep them out for the 8 weeks to kill the ich so they don't keep getting it. No need to keep dosing herbtana, the ich will die by themselves.