My own personal method when quarantining a new fish was to start them off in the Quarantine tank with water directly from doing a water change in the display. I let them settle for a couple of days and then begin a hypo-salinity period
http://www.advancedaquarist.com/2007/6/fish I keep the salinity at 1.009 for about a month, then start SLOWLY bringing the salinity back up over the course of a week or two.
When it's all said and done the fish will have been quarantined for about 6 or 7 weeks.