Blue tang lost colour and unwell

[Leeleonaallen]

So my blue tang Who’s on qt tank for 2 days I’ve had her and she seemed ok at first now I’ve noticed she’s laying down a lot and has gone so pale all of a sudden I. Gutted cos I e just recently lost one I can’t lose this one aswell I’ve checked the water its ok, the copper levels are on to! What am o doing wrong again