Wanted answers to this as well.... Cycled my tank with established rock from my old tank. Added some fish after a bout a month. Seemed fine... then one got sick and spread the disease to half the other fish... All that had Ich died, but the other half the fish never showed any sign.
So... There has been no Ich signs in my tank for 6-8 weeks, but the tank was never fallow (fishless). When might it be safe to add another fish?