definitely quarantine. If its not too late, ie it hasn't had the ich long, do the fresh water dip. If its been awhile, then I'd go with copper. Dips are hard on fish, at least harder than the copper, imo. Raise the temp in your quarantine to speed up the life cycle. If you do intend on a fresh dip, then make sure you buffer to the same ph, temp, and salinity. Good luck!