Inverts are species such as shrimp, clams, and starfish. Some people set these up with no fish. Angel fish are prone to nip at and eat certain corals. Not all angels do this, but its best not to take the chance. The equipment that you will need for a salt tank are filter, skimmer, powerhead (for water movement), and good lighting for corals. The skimmer is probably the most important peice. A good brand for a tank less than 55 gallon would be seaclone or prizm. For larger tanks a berlin would be a good choice. Most people use anywhere from 2-4 powerheads to get good water movement. A good brand to look at is maxijet. When you are ready for corals you will want good lighting. As a genreal rule you want about 4 watts per gallon. There are several types that are good for corals. Power Compacts or PC's are the 1st and least inexpensive. VHO or very high output is another type, and I think most have this type. The last is MH or metal halide. These are the most expensive, but reproduce natural sunlight better than the other types. They also produce alot of heat.