chocolate (mimic) tang

My Mimic tang shows white patch near lower abdomen and white dots on her fins after I added a blue tang yesterday after QT for 3 weeks. Please advise next steps

In the now two days I’ve had my baby mimic tang, it was immediately clear that my sleeper goby and him were buddies. I haven’t seen them far from each other since moments after the introduction. Including an adorable “tour” by the goby, to places the tang couldn’t fit there’s no harassment, and...

This ones been in 20 gal qt for 48hrs 1 dose of cupramine, white patches still present. Should I go through with the second dose of cupramine, or water change and switch to Furan-2?