A QT tank is a tank set up to hold your new fish to ensure thier health and to reduce the threat of contaminating your main display tank. You would generally set up your QT tank by taking some LR or filter media,etc from your main tank to get the bio filtration going. Then add hiding places of inert materials for the fish to feel secure, ie. PVC, ceramics, etc. You must cycle the QT tank as the fish will stay there for a reccomended 2 weeks as long as no signs of disease or stress arise. If problems show up, you must then treat and re-start the wating period. HTH.
Kyle