The term quarantine can mean different things to different aquarists. To some it's a sterile-looking, medicated,bare tank that houses new fish for a day or two to see if any disease develops, and to others it's a second fully set up smaller tank that maintains new fish and invertebrates for several weeks to be sure all is well before introduction to the main tank. Both methods have their advantages and disadvantages. The bare tank allows effective use of medication, good observation of the fish, and the opportunity to keep the tank bottom clean. However, the fish cannot survive long or well in such a set up, and the water should be discarded after each use. In my opinion, the bare tank finds it's best application is a treatment tank, for use when a disease has been detected and a course of medication is determined. The determination of the specific disease is crucial to the utilization of the specific medication. Use your LFS's suggestions with caution on treatments, as some if not most of the time, the aquarist knows more about the fish and disease than untrained LFS personnel. I have heard all too often to use copper when I have said "The fish is sick." They do not ask for the visible symptoms, they just say to use medication not necessarily useful and could be dangerous to your fish. It's like going to your doctor with a nose bleed, and he prescribes Viagra for you!
    A small tank, 10 to 15 gallons, set up with an under-gravel, biological filter and a natural tank decor, is more functional for quarantine than a bare tank. It allows a new fish to be maintained under good aquarium conditions for two to four weeks to get used to the water, the tank routine, and available foods away from the competition of the main tank. If a fish does bring a problem home with it, this should be evident within 2 or 3 weeks and, depending on the disease, treatment can be effected in the quarantine tank or in a bare treatment tank. A small quarantine tank is a lot easier to keep free of disease than a large display tank, and can be used to brighten up another corner of the room. Also, if necessary, a 0.2ppm copper treatment level can be better maintained in a small tank that does "NOT" contain calcareous gravel or rock and decorations. Following the simple procedures of selecting top quality fish, giving a one minute freshwater bath before introduction to a tank, providing a 2 or 3 week stay in natural type quarantine tank, feeding a varied diet, and adhering to a good maintenance schedule, will give you a marine tank relatively free of death and disease.