I had a QT set up for a long time while I shuffled fish into my aquariums. It made more sense at the time than taking it down and setting it up all the time. Now I just set it up when I need it. I keep it simple. A few days prior to getting an fish, I take the filter pad and put it in my DT sump along with the sponge on the end of the filter intake. Then I use water from my DT tank to fill the QT, to ensure similar parameters. When I place the filter and sponge in the tank there is enough bacteria to maintain a light load, a few small fish, or one big fish. If you need more bacteria you can put a shallow tray of live sand in the tank, this way you can take it out easier if need be. And as mentioned before, my filter is 2x more powerful than needed. I use a 10 gal tank because I like many small fish over a few large fish. I use a 20 gal filter with a heater, and digital thermometer. I do 2gal (20%) water change every 2-5 days depending on load and test readings. Also I do a 45-90min drip acclamation followed by a 15-30 min temp acclimation on all fish as they come into and leave the QT tank. It doesn't matter if it's a $5 chromis or $100 tang, they all get the royal drip. I'm by no means an expert but that's what I do and it has worked well for me.