I did (still do?) have ich for 5 months. I QTd the fish and run the tank fallow for 1 month, put them back in and 2 days later they broke out. I've done everything, hypo, KickIch, you name it . So I decided to run the DT fallow for 2 months and do some changes while fish were back in the QT, hence I changed out the substrate, dropped the salinity to 1.009 to help kill ich (massive water change), added live rock. Doing the huge water change (75%) basically killed the biological filter and adding the LR
brought me to my original question of curing the LR
Oh, and believe me, there is NO bigger proponent of a QT than ME!! I have 2 sets of QT equipment.