Completely disagree. Hypo can and most likely will kill the inverts. I'd leave the inverts in the display and remove all fish to a QT to treat with hypo/refractometer to test or copper with proper copper tests. I'd leave the display fallow for 6-8 weeks.
That is why you should use prevention versus treatment after the fact.
I Just talked to a Marine Bioligist From My LFS and they said Ich is always in the tank. Theres really nothing we can do.