Maybe I’ve been lucky or maybe flasher wrasses are more tolerant? Mine have always been ok with cupramine.My personal experience - tangs aren’t overly sensitive to copper, especially copper power. The wrasse is a different story. Remember the white spots of velvet is the aftermath of velvet, so while it may seem he’s in a “safe zone” with no visible signs, it could be the opposite.
again, personal experience and opinion, if you’re using copper power take it up asap.