When I set up my QT, I'll use a 10 gal
tank and use RO
water. The salinity for my display tank is normally 1.024 but in my QT, I'll start off with 1.019ish for about a week then down to about 1.015 or so for about another week (or longer if needed) and keep regular temp. Don't put anything in the tank such as LR
or substrate. Leave the bottom bare. If you want to put a couple pieces of PVC
pipes so the fish will feel protected, that's fine. Once the symptoms subside, then gradually increase the salinity again. I usually keep them in for at least three weeks or so. At least one week symptom free before returning to the display tank. Sometimes (for parasites) the lower salinity will be enough to treat the problem and you won't need medication. If you do use medication, don't use carbon. It will neutralize the medication and it won't work. I've also used a hang on filter (whisper) for filtration. If it comes with any filter cartridge, you can take the carbon out and put in an ammonia filter sponge (cut to fit) in the filter which will help with any ammonia build up too. I also do a 10% water change every week. Hope this helps.