I ordered a purple tang from live aquaria’s divers den and it arrived a week ago. I put it in a QT tank with copper safe and it developed a white dot near its tail that might be ich. Copper is now at 2.00 ppm (checked with Hanna checker) and tang is still eating very well, also started adding metroplex. How long should I keep it in QT at these levels? Is there anything else I should be adding or doing?