I've got a blue regal and a purple tang. My blue seems to have white spot every other week but my purple only had it briefly last year and it never has shown up again. I believe feeding good and keeping things stable have worked wonders. I'm sure over time there immune system has gotten stronger. I feed a very wide diet and I truly think it helps. It's unsightly to see a few spots on blue tang but she's fat and happy so I leave it be. It has never spread to any fish in the tank. You have to decide if treating is the right thing to do for your fish. I remember years ago that I would jump at the first sight of white spot or something wrong and treat the fish. Every fish took the same porcelain trip. Not saying it will happen to you, just sharing my experience.