I have had my 72 gallon bow front up for about 6 weeks, cycled with existing sand and lr from prior setup. I introduced chromis and doing well, clown fish doing well, so I added a blur tang and a blond naso. The fish were eating and doing well with no complaints, then 2 days ago the blue passed, and now my naso is secluded. She eats here and there, but spends most of the time hidden away darker in color with white stress spots.

Lost not sure what is happening, water tests daily show no issues all readings are perfect occasional .20 spike in nitrate that corrects itself. Any ideas?