New to the hobby... Have this blue tang and a yellow tang in 20g QT for four weeks now and the blue has had this discoloration the entire time. Cycled tank and no ammonia or nitrites/nitrates. Ph is 7.6 and 36.6 salinity. Treated with copper for three days early and then recently With melafix for 9 days now. Water changes (25%) every 4-5 days. Could this just be stress after all this or do I need to treat differently?? I have a 125g dt waiting for them with two clowns, a fire fish and a spotted goby so don’t want to risk my other fish and many corals by putting them in if any risk of them being sick.