Lighting is one of the most important aspects. The lighting depends on what kind of corals you want to keep. If you choose soft corals (leathery corals), you must have at least 0.6 watts of light per liter. For stony corals, it is higher. Here you need to assume at least 1.0 watts per liter. More is always allowed, but this is the minimum requirement if you want to be able to accommodate the corals well.