I definitely keep a QT tank..... I have a 20L that I picked up at one of Petco's $1/gallon sales and built a stand for it. I have a small heater, cheap HOB
filter, couple of old freshwater fluorescent lights, and eggcrate lid cut to fit. I have a 32 gallon trash can that I maintain 25 gallons of saltwater mixed & ready with heater & powerhead, in case I need to do a large pwc
on my DT or an emergency quarantine, and I keep a small bag of Biomax in the rear sump of my tank so it always has BB in it (rinsed out occasionally in old pwc
tank water to clean out any gunk).
If the need arises, I can pull out the Biomax, drop it in the HOB
filter, fill the 20L with proper temp & salinity water, and have a QT tank up & running in 10 minutes or less. When not in use, I keep a garbage bag over it to keep the dust out.