your only option is moving all the fish to a separate tank, treating them with copper or hyposalinity, and running the display tank fallow (fish less) for 6-8 weeks
Ich can be managed with healthy fish and systems. Except for some like the powder ich, and Ichillies tangs. However there is a point of no return where meds are the only possible saving measure.
Please think twice before doing hypo - I’ve done that before and in the end lost 90% of my fish anyway. The fallow method works — treat fish with copper in another QT. Make sure to get a good copper tester like Hanna. Watch out for ammonia during treatment.
Good luck!
