Am i doing this wright? is there anything else i should be doing? thx

Most people use a bare q tank, especially when treating ich since the life cycle involves a dormant cyst component. You can actually help "treat" the ich by removing cysts via a water change, much easier to do in a bare tank. Add something like a cheap plastic pot on it's side for a hiding place, if you really need something.

I have three thoughts:

Some tangs are averse to copper and are better treated with formalin, if at all. I don't know of your tangs fall into this group or not. I don't have enough information.

"A fish that eats is a fish that lives." Feed the sick fish liberally and offer a varied diet. If they are eating voraciously, they have a great chance of fighting off their attackers through natural processes.

Finally, the parasite afflicting your fish exists in many, if not most, tanks. If the fish didn't show extreme infection, I would have left them untreated where they were. I would not have stressed them further by catching and moving them. What I would have done, if I could, was make sure that they were not being picked on by other fish and they they had plenty and varied food throughout the day, including grazing food; live or dried algae in a clip.

I hope this is helpful. Best wishes to you and the tangs.

Jeff