You
must keep ammonia at 0
at all times with marine animals. Even
slight traces can be harmful.
In a QT you can accomplish this 1 of 3 ways:
1. Biological filtration
2. Water changes
3. Ammonia reducer such as Amquel or Prime (however, you
cannot use an a
mmonia reducer in the presence of medications such as copper)
If you haven't already, I recommend reading this guide:
https://www.reef2reef.com/forums/fish-disease-treatment-diagnosis/189815-how-quarantine.html
Under the section "Ammonia control", I discuss how to use a cheap HOB power filter as an effective bio-filter in QT.