In your QT you want too keep the temp the same as your display tank, its best to use water from your display to start the QT tank in the first place since it will be the same when you transfer the fish to the display and it will help minimize stress. You would most likely want to keep the QT tank bare bottom (no substrate) with some pieces of PVC pipe or some other inert object like a flower pot, just for the fish to hide. Water changes must be done very often, sometimes even daily unless you have an established bio filter running 24/7 in the QT. Water changes are done with water from the display tank. There must always be fish in the QT tank if you are running a dedicated bio filter or the bacteria will just starve and become very weak and will be of no use.
HTH