Should I be dosing my tank with any kind of chemicals they've got for sale such as magnesium or zinc or whatever all of those little bottles at the lfs are? If so, which ones and how often? I've got a 20gal with 4 fish, a few polyps and a clean up crew of hermits, a snail, and a cleaner shrimp. New to the hobby, or new to saltwater anyway, and don't want my fish to die or be too unhappy