How long to leave quarantine tank alone?

[MitchM]

My experience with Ich is that it is always present.
It can show up on some of my fish if the fish are stressed or if the water quality drops for one reason or another. A return to good quality water conditions makes the symptoms disappear.

I've never had a tank without fish for any length of time, but the Ich parasite DOES require fish to be present in order to complete it's life cycle.
30 days is the typical Ich life cycle, but I'm sure it can be lengthened by lower temperatures or other factors

Ich isn't the end of the world, just make sure that your fish are living as stress free as possible, you feed them well and you keep your water quality excellent.