I'm using carbon in the HOB
on my QT with my fish undergoing hypo treatment for ich however I did not use any meds and will never use copper (Nasty stuff). My salinity is 1.007-.009 in the QT and the fish are doing fine in case you were wondering about it. Before you start you must have a refractometer because hydrometers are not nearly accurate enough. Just remember to to start at a normal salinity level and gradually bring the salinity down by changing 15 to 20% of the water with treated RO
every 12 hrs until you reach 1.007 to .009.
After treatment you must bring up the salinity much slower to allow the fish to adjust because the higher the salinity level the more difficult it is for them to breathe and they need more time to adjust. When you are reducing the salinity the opposite is true it becomes easier for them breathe so they actually endure less stress on the way down then on the way up.
BTW good luck.
Oh yeah, from all of my research you should have a dedicated tank for meds and copper treatments (Hospital tank) that is different from your QT.