I think leaving the tank fallow for 2-3 months is plenty as long as you gravel vacuum the substrate weekly or bi/weekly. A Formalin bath followed by a 5-10min fw
dip before putting in qt. How long can black ich survive without a host? Dunno, but either does the article. It just states that it can survive for "several" months without a host meaning more than 2 months, but not necessarily more either. Noga states that some strains of Cryptocaryon "theronts requires that aquaria be left without fish for at least 3 months to be rid of the parasite." I guess what to take from this is you always qt your animals because strains of parasites and diseases always seem to find another way to baffle us just when you think you have them cornered.