Forgot to mention about setting up the Quarantine Tank:
A quarantine tank is often smaller than a regular tank, and because it is to serve only as a temporary home, this is acceptable. You must first obtain a small tank. A ten gallon tank will be acceptable for one or two fish. You will also need an airpump and airstone, plus airline tubing. Aeration is especially important in a quarantine tank because the size of the tank is often smaller than usual, and medicines sometimes take oxygen out of the water.
Lastly, find something to cover your tank with so that the fish don't jump out. Nothing else is needed. The quarantine tank should be relatively bare. This will make cleaning much easier. Your fish may be reassured by the presence of some plastic plants or hiding places, however. You may wish to include some of these. Lead anchors are sold that can be used to hold a plastic plant in place. Also, since the fish is reassured by a dark bottom, you can place the tank on top of a dark mat or piece of cardboard if you wish. This will show through the bottom of the tank.
If you do decide to use a filter in the tank, make sure there is no activated carbon in it.
Place the quarantine on some steady, flat surface which will be able to hold the weight of a full tank. It is a good idea to put some water from the main tank into the quarantine tank to avoid stressing your fish. If your main tank is very big, this will be no problem. If your main tank is somewhat small, adding just a little of the water will also help. Take water from the top of the main aquarium. This water is always the cleanest.
When your quarantine tank is full, attach the airstone to the airpump with the plastic tubing. Then place it in the tank and weigh it down if necessary so that the stone is at the bottom of the tank. Next, add any decorations like plants or hiding places. Make sure all of these are soap-free and aquarium-safe.
If you decide to install a small filter, do so now. It will help to keep the water clean. If your purpose is to treat sick fish, don't add any filter carbon. If you are using the quarantine tank to observe new arrivals, carbon may be added.
Note - any equipment used for the quarantine tank should not be shared with the main tank. This aviods the possibility of passing infection to the main tank.