microbubbles,
I keep all my fish in QT for a minimum of two weeks. How long they stay in QT is determined by the fish's health problems. Even if I buy a fish that looks perfectly healthy from a great source I still QT for a minimum of two weeks. As far as hyposalinity goes I recommend you read this thread link as this is the method I typically follow:
http://www.reefaquariumguide.com/forums/showthread.php?s=&postid=348271#post348271
As far as your questions on tangs go....I can't really answer that. I don't keep tangs and I really don't have an inclination to do so. I'm almost 95% dedicated to wrasses and that takes up most of my time and space.
I'm sure tangs are great SW fish but they just don't capture my attention and as I heard from many SW experts....they are an ick magnet. Seems like they are more prone to the problem and its hard to get rid of with them. So I really wouldn't be doing you any favors to give medication suggestions on fish I know little about.
I'm sure some of our friends in RC can give you better suggestions than me on this subject.
mike89t,
glad to hear things went well with your formalin dipping. I'm sure you were very concientious about how you dipped your healthy fish. I don't mean to say that formalin is unusable. But it can be a very dangerous liquid to use with wrasses. Specially since wrasses for the most part don't ship well in containers and end up having a lot of stress induced illnesses in the shipping process.
If your wrasse has been in a healthy tank at a LFS and he comes home with you healthy....then they very well may handle a very quick formalin dip as the one you mentioned. However, most wrasses that have been shipped roughly won't handle a formalin dip.
All anti-parasite medications or procedures (hyposalinity , copper, special dips and formulas) are stressfull in one way or another to the fish. But IMO Hyposality in mild cases of ick is probably the least stressfull. I certainly wouldn't suggest dipping a wrasse in formalin as soon as he comes out of the shipping box or shipping bag.
As a matter of fact, unless the fish has an extreme case of ick or velvet I think the best thing to do when he comes out of a shipping box is to place him in a QT tank where the water has not been treated yet. What I mean by this is the salinity has not been lowered, there is no medication. Simply clean system water from your main tank that has been poured into the QT. Acclimate the fish and then release him into the QT with clean system water. Have a good filter running and a strong air stone going. Immediately shut out the lights and let the fish sleep in the dark for a day without bothering him. After a day or so assess his health and then start lowering the salinity or adding medication as needed.
In my experience wrasses are at there most vulnerable spot health-wise when transfering. Therefore I think they should be "babied" through this process. Once they are healthy and installed in a tank they become nearly bulletproof putting up with mild parasite outbreaks as if they were just a mild headache.