Many macroalgae aren't that picky, requiring only light and the nutrients that the other livestock produce. They can vary, though. Chaetomorpha and many Caulerpa species can thrive in most conditions, while species like ulva seem to need heavier loads of nitrate and phosphate.
Vascular plants, i.e. seagrasses, need a good substrate, between 3 and 6 inches depending on the species. Mud, or a rich substrate seems pretty important to keep these guys happy.
Sarah Lardizabal, who is something of a marine plant expert in the online world, wrote a nice article for Marine Depot some time back: Marine Plants.