I run a 20G QT that I maintain continuously for two reasons. First, it easy to maintain as it’s simply a HOB filter and thermometer. I use water from my DT tank changes as water replacement in the QT, and the filter box usually just holds a sponge for bacteria. Second, it’s great to have available if a fish starts to show any signs of illness. Easy to treat and observe. I’m still adding fish so even without medication (not starting that debate) I still have a place for fish to be observed and see how they are doing before going to DT. And since water characteristics are similar and temp same it’s easy to just drop into DR