My understanding of a QT is that it is literally just the aquarium and a powerhead, no sand, no rocks, no filter. You should put a piece of pvc pipe in it so that the fish has something to hide in, and just do water changes regularly to keep it clean. I think this is the type of set up you need if you are going to treat fish with copper or other meds. If you go the hyposalinity route, you might be able to do a better set up than this, I'm not sure. I do know that you can't just QT fish to get rid of ich, you have to actually treat them for I believe 8 weeks before adding them to your DT. I am sure someone wtih more experience will chime in!