QT don't have to be set up all the time and they don't need to be a tank. You can use a large Tupperware or storage bin. You need a spare heater, filter and the 'tank'. You can run the quarantine filter on your established tank then when you need it it's already cycled. You can just move it over to the QT. If swapping filters from tank to tank be aware any disease in one tank can be transferred to the other. If you treated a contagious disease its a good idea to replace or disinfect the filter media before moving the filter back to the healthy tank to seed with bacteria again. Another option is to keep the tank set up and empty. You have to dose pure ammonia every few days to keep it cycled.