If you aren't going to qt, set up with a potent CUC fed handsomely for four to five weeks, to prep the tank's biosystem to handle a load, and then get all the fish you're ever going to get and put them in at the same time or real close together---using all the skill and observation you've got not to buy from a 'sick' tank, including how they're piped together. Do it once, cross your fingers, and be equally careful adding corals. Don't buy coral from a fish-sale tank or one piped to it. If you didn't get hit with parasites, fungus, bacteria, or virus in your one fish purchase, and never add to it again, your luck will be FAR better than the guy who shops the fish store weekly to get some other fish to try.