have a read of this thread and ICH;
http://www.reefland.com/forum/marine...-ich-help.html
the ich parasites can latch onto anything (ie live rock/sand from you display)
with that said maybe run the QT with nothing more than a fresh set of filter pads (to keep the tank clean) and regular water changes to export the waste.
are you removing all of your fish to QT them?