Blue Regal with ICH!

[mark]

Getting the impression it's always going to be around unless you remove all fish and treat in a QT (hypo-salinity or copper) and let the tank go fish-fallow.

There's a chance the fish can get over it and it won't show up again or it could kill them all. Risk you're taking if you try to wait it out, fish might be too weak for treatment if things start going bad.