marine qt tank

I usually recommend leaving some piece of filter material lying around, be it a sponge, biowheel, etc. to leave in the main tank/sump for a while. While you may not want one all the time, leaving it in for several weeks prior to purchasing your fish is ideal. A simple HOB or canister filter is sufficient for any filtration, along with water changes. It is also necessary to monitor water quality closely. You can use non-porous decorations, plastic plants, etc., to give fish some cover. A light isn't necessary, but helps in some cases. I'd look for at least a 10g aquarium to use as a quarantine tank, too, depending upon the fish species (and number of introduced specimens).

Well, if it is just QT, then no dosing, just observation. If you are going to use a prophylactic, which I don't personally think is necessary (but is if you want 100% parasite free tank), then hyposalinity is usually the best choice. The duration for that would be 6-8 weeks.

As far as durations for various medications, that varies depending upon the drug.

I prefer cuprimine myself Easy to use and the fish acted perfectly normal for the 5 weeks they are in QT.

Cupramine is good, too. It's the only copper-based medication I ever recommend.