When I have used a qt, I have tended to do it bare of all ornament and sand and rock, except where a fish needs to hide for its comfort. I put one rock in, for that. I keep the tank empty and ready, with its equipment.
If you are needing to take an injured fish from your display tank to qt, take tank water with him so he will not have the stress of a water change---unless you suspect the quality of your water is the source of the problem, of course.
If you are qt'ing a fish you have just brought in from the store, do not use the water he came in: discard all of that under any circumstances, after you have prepared new salt water AND drip acclimated him in his bag. You could equally well use water from your tank, [but it will carry chemical 'messages' from your inhabitants.] And it is probably quicker to prepare new water: it has to be made up somewhere, if you have filled an entire tank with it, so it might as well be new water. It's not much difference for the fish.
