Saltwater aquariums are communities of fish that inhabit water with a salinity of 1.020-1.025 sg. There are many different types of saltwater tanks, each one with specific requirements. Saltwater aquariums usually have a combination of fish, invertebrates, live sand, live rock, soft coral, and hard coral. Saltwater tanks need a longer period to fully cycle and can take up to 4-6 weeks of cycling before adding fish. Some saltwater fish/invertebrates are incompatible with others, just like with freshwater aquariums. Saltwater aquariums need a filter, heater, and protein skimmer. Weekly 20% water changes should be performed.