The advice about having a QT set up all the time is good advice. When I first set up my reef, I set up a QT and tended to never use it. The fish in the reef, which did on occasion show signs of ich, were never killed by it and it passed on its own, so I ignored quarantining. BUT.....then I set up a FOWLR. This tank was just a horror-show of losses. If it wasn't ich, it was velvet...frequently both. I lost so many really beautiful fish. Sometimes, the disease was difficult to identify. I think that was when it was velvet alone and it killed the fish very rapidly. SO...the QT!...I figured that I would have to quarantine when I acquired fish for the FOWLR, and I did. And, even though I quarantined new acquisitions for over a month, shortly after I put them in the FOWLR there would invariably be an parasitic outbreak. Finally, I took all of the fish out of the FO and put them in the QT and treated the QT with copper (using CopperSafe, in accordance with its instructions. It was successful in clearing all of the fish that I put in the QT. I left the FOWLR empty of fish for almost 8-weeks and then put all of the fish...with none other than the ones in the QT...back in the FOWLR. Withing three days, velvet!!
At that point I decided that I would either have to apply copper to the FOWLR itself...or...change it over to a freshwater tank.
I decided to treat with copper, again using CopperSafe in accordance with its instructions, and I haven't had a problem since.
I guess the moral of the story is that for some people...at least for me...a fish only tank isn't viable unless there's copper in there with the fish. Quarantining alone, in my case, for just about 8-weeks wasn't enough to prevent a parasitic outbreak. I don't know why...it just wasn't.
I'd recommend copper right in the FO and that's that for me. Of course, you have to be sure to never use the tank to keep many inverts. But oddly enough, I actually have a constant population of pods in the sump even with the copper. I can't explain that.
That's my experience with a FO tank. It wasn't pretty...but now...with copper, it is.