Minimum of 30 days, but 6 weeks would be better in Copper. I am going through the same thing and I have been reading everything I can. My Majestic Angel and Clown are in QT with Coppersafe. Full infestation on the MA. Been 2 days and she is looking better.
With the life cycle of ich documented, it is apparent to me that ich is only vulnerable to copper in its free swimming stage--this being the reason why the cysts don't just fall off in the beginning and why a full 30 days is needed to be assured that all ich has been destroyed.
Also, I have noticed that over the years, the fallow period recommendation on the main tank has gone higher and higher as more knowledge of Crypt has been discovered. I am reading 8 weeks as the fallow period, but also have read that ich has been shown to live up to 72 days in a fishless system!!!
where's me money