Saltwater aquariums, also called marine aquariums, imitate marine or ocean environments and house various marine plants and animals. They contain water with a salt level between 30 to 40 parts per thousand (PPT), the same level as natural seawater. Basic saltwater systems include a transparent tank, filtration system, skimmers, and hood lighting. All components are made of coated material to prevent corrosion from the saltwater. They can also contain live rock, which are covered with healthy algae and support smaller forms of marine life. Saltwater aquariums are considered more challenging than freshwater aquariums because they require more maintenance, equipment and water changes.