This wasn't exactly my point. I do believe in an ich free tank, but I also believe that many tanks people think are ich free are probably not. I also believe that this is much harder to achieve than merely observing in a qt for 6-8 weeks.
Given the choice, I would rather have an ich free tank than one that might have it EVEN if it is subclinical.
If that means treating healthy fish, I would.
However, given examples of failures of treatment of both hypo AND copper AND the possible complications of the treatment itself, the question becomes DO THE BENEFITS OF TREATING ALL NEW FISH OUTWEIGH THE RISKS OF TREATMENT.
When I was only observing for 6 weeks, it obviously was. Although running a second tank is labor intensive for sure.
Now treating with copper or hypo or transfer method, the decision has to be made for each person and really comes down to HOW GOOD ARE YOU AT TREATING FISH. There is a learning curve much like learning to keep a good reef tank when treating fish. And in most cases, there will be causalities.
my 2cents...