Ich aftermath... what to do now?

[asylumdown]

At this stage, it looks like the fish in your QT have developed a certain amount immunity to the parasite, which is why you're no longer seeing any active pustules. Acquired immunity has been demonstrated in a bunch of fish in the literature, but the parasite is definitely still in your system.

If you have no plans of going through the extremely intensive and time consuming process of taking the remaining fish out and treating them in QT while fallowing your tank for 10-12 weeks, your best bet for re-stocking is to not buy any fish that are known to be highly susceptible to ich, as it's in your system. IE, don't buy any more tangs.