Tangs are generally not "sensitive" in copper. Although following the instructions on the cupramine bottle introduces the copper rather quickly IMO. So I always recommend to figure total dosage and slowly ramp up over 5-7 days split into at least 2 doses per day. This helps them adapt to the copper treatment better.

Are fish sensitive to copper?

Many fish are sensitive to copper and may become intoxicated at concentrations required to control pathogens. Copper concentrations in treatment tanks must be measured frequently to ensure that levels are therapeutic but not toxic.

What marine fish are sensitive to copper?

In my Advanced Marine Aquarium techniques book, I list: sharks, rays seahorses, mandarin dragonets and jawfish as being very sensitive to copper.