Been there done that. I wouldnt do it again. I let my tank sit fallow for 9 weeks. Put the fish back in and they still got ich. Ich can sit dormant for a long time. I also lost a couple fish while they were in QT(3 wrasses).

I actually pulled out my fish to put them in Copper as they had Velvet. But figured I would take out ich while I was at it. So I coppered my fish with cupramine in a 50gish qt and just let the display sit.

Since you are only dealing with ich I would just do what funkyseamonkey did and bump the feedings up a little.

If you still want to do the qt I would do it alot longer, probably 4 months and get a bigger qt just so you dont have to do water changes so often.