I somewhat disagree w/ a 10g tank as a quarantine tank DEPENDING on the circumstances. A 10g tank is fine if you are only going to be keeping or purchasing smaller fish. If the fish are going to be a little bit larger like a 3 or 4 inch long tang then the 10g tank isn't going to cut it. I say get as big a QT as you've got room for. a 20gL or 30gL may be a better option if you plan on getting some bigger fish.
I made the mistake of trying to quarantine a 4" powder blue tang in a 10g tank one time. Aside from the fish being too big, tangs need a lot of swimming room and the 10g tank didn't have it. The tang stayed stressed and died before the QT period ended.
The bottom line is that you have to have a game plan and know the requirements of the fish that you plan on keeping BEFORE you buy them and before you set up a QT.
A QT should be a very simple system. Bare bottom, no LR and a simple filtration system. A tupperware container, with bioballs and a powerhead make a great filtration system for a QT. You should put some PVC fittings in the tank to give the fish something to hide in. This will help to reduce their stress level a bit by providing some hiding places. Here's a pic of a home made filter from one of our members.
