Steve, I agreed 4 weeks with hypo should be enough. It must be the fallow period not enough.
I have not move my yellow tang to QT
yet because he is enjoying the better quality water in the main tank. And he is definitely looking healthier even though he has ich. However, I also observed he is getting help from my cleaner shrimps. The ich has been clearing up , with one or two cropping up each day, but doesn't look like manifesting itself.
Previously I had a couple of neon gobys which I was told by my LFS
will control the ich. That was until they got infested and died. So neon gobys are just as vulnerable as other fish. I still believe it is reoccurring ich that I have got.