Bubble, bubble, there's toil and trouble setting up a 200-gallon saltwater aquarium on your own. If you're determined to do it, pay a visit to the Buy and Sell forums on the Web site of the Dallas/Fort Worth Marine Aquarium Society. You'll meet fellow hobbyists who can outfit you with price-savvy used equipment and stock, from tank to Tonga branch and metal halides to Montipora, often at 50 percent (or less) of the cost of a new item. And considering aquarists' love of upgrading and the large membership of the forums, you're likely to find that the item you want (or someone who wants to buy your item) is just a short swimming distance away.