I share your concern as well. Time will tell.I'm keeping a very close eye. I'd previously dosed H202 for 2 weeks for the royal gramma when he first showed spots, now he has none... maybe 1 spot every few days if at all.
That's my only concern here, the blue tang is quite young, and so I imagine it's immunity is not as strong or developed as yours. Hoping I can manage his condition to get him to where the Royal gramma is now... ideally down the line when possible I will absolutely QT all fish and go fallow. Must look into the green machine you mention, seems more practical than plumbing a UV in. Thanks!
I’ve QT every fish that ever entered my system and STILL managed to get an infection. I was adding dipped corals throughout, so I guess maybe.
I think early infections are less of a problem in mature systems, with strong fish.
If they eat normally, this is a super big plus!
Best wishes