I don't quarantine or recommend it. I know this goes against what many people recommend but IME 95% of QT tanks are not at least as good as the DT in which case livestock is are more stressed in QT than in the DT and stress=illness. If you can keep the water quality up with frequent water changes (using water from the DT ideally, to get him used to it) and he is eating well you are okay.
What fish are in the DT now?