Hi,
Everyone has their own way. I don't keep my QT up and running because I seldom have to replace fish and my tank is stocked. I did keep it going when I was stocking my tank that first time, since every time I put a fish into the display, I was ready to add the next new fish to the QT.
I keep sponge filter media running on the display tank...when I need a quarantine or hospital tank, that material is used in the HOB filter, which means instant cycled, for that one fish that needs to be in it. Very little good bacteria is in the water, it's all on the hard surfaces, since there is no sand used on a QT/HT, the loaded with good bacteria media is all that's needed. If you run a sump system you can even toss the intake tube in a chamber below, to be covered with good bacteria as well.
If my 10g is being used as a quarantine, I also add macro algae (caulerpa prolifera), in a hospital tank the macros can't be used. Macros help to keep the water quality good, and that makes it worth it's weight in gold when it comes to small tanks. If the new fish needs treatment, I remove and toss out the macro before I dose the medicine.
