For fish QT, the most common method is copper followed by prazi. You can also feed medications to fish while they are in copper (such as general cure with focus, etc.).
A lot of it depends on what you are wanting to treat for, how risky you want to be, and how
I get fish from pre-QT vendors (at a price) so my QT is a 10 gallon tank with a HOB filter with ceramic rings and carbon (I remove the carbon for part of the time) a small UV (green machine that I had laying around rated for 75 gallons), a small wavemaker, and a little ball of chaeto to help keep the phosphates low. I first dip the coral and remove the frag plug or brush the plug with a rough cleaning scrubber thing, then I scrub the parts of the skeleton without tissue (this only applies for LPS), swoosh them in the dip, and then put them in the tank. I have some brightwell koral recover that I use for a week mainly because I have some lying around. I then keep the coral in for at least 4 weeks though will do so for 7 if it came from a place where marine ich was likely to be present. I then dip it again and put it in the display after that. While in QT, I dose coral food.