Quarantine tank questions

[SD_Reefer_Madness]

I recently upgraded from a 20 gallon IM nuvo to a 65 gallon JBJ AIO. I’ve moved the majority of live stock to the 65 gallon DT and I eventually want to use the old 20 gallon tank for a quarantine tank. I’ve found the humble fish articles, but it covers setting up a QT from scratch. I’m wondering if I set it up right and removed most of the live rock, a bit of sand, and of course the rest of the livestock, can I use the already cycled system as a ready to go quarantine tank?

 

[Idoc]

It's best not to have rock or sand in a quarantine tank that you plan on using to medicate fish. These things may absorb the medications making therapeutic levels difficult to maintain.

If only using it for observation without meds, then it should be fine.