Here's the thing, unless you qt corals and inverts, or are rlly diligent on removing every nonliving tissue or material on the frag, colony, etc and brushing down any shells, ich is bound to get into your tank whether you realize it or not. Most people don't have the resources to setup and maintain two qt's and maintain reef level params in one of them. It get's very expensive in an already pricey hobby. I think your best bet is to treat your fish this once with copper power or something similar at the therapeutic level for 30 days in a seperate tank in order to have a clean slate. Depending on your tank size, employ live rock, phyto, pods, bacteria, and extra nutrients and vitamins in your fish food. Adding a UV would also significantly help. This helps add biodiversity to your system, and with the addition of the UV, ich is almost negligible. I would still qt any fish and be diligent about brushing and removing dead tissue and frag plugs in order to prevent some of the nastier diseases like velvet, brook, uronema, etc.