I believe you mean what is the difference between a reef tank, FO (Fish Only) and FOWLR tank (fish only with live rock). Fish only is as the name implies and is geared towards showcasing marine fish. They are usually lightly decorated and more forgiving when it comes to lighting, flow and water quality requirements. Stepping up to a FOWLR tank adds the live rock to supplement filtration using the nitrifying bacteria typically found in properly cured and cultivated live rock. Lighting must be increased to maintain good coralline algae growth. The reef tank is the most expensive and demanding form of the saltwater aquarium, it is based on showing off corals and invertebrates with a light fish load (typically). Live rock is used at about a pound per gallon of your system to provide heavy natural filtration and in most cases, specifically on larger tanks, protein skimming is recommended practice as well as frequent water changes in the 10-20% per month depending on your bio-load. Lighting must be carefully selected for the proper growth of the corals you wish to keep, (Softies, LPS or SPS) and is usally much more intense as most corals produce the majority of their food through photosynthesis. Water quality must be monitored and kept pristine for these species to survive and the typical flow or water movement through the tank (goal) is roughly 10x the volume of the aquarium system as a whole but i have seen instances where people move double or triple that depending on the corals they are keeping. This includes tank, sump or refugium.
This is a very basic description anyone else please chime in but hopefully this is helpful.
