in areas without access to clean sea water. Air driven, counter-current protein skimmers and reliable submersible electric heaters were invented in Germany. Various advances in filtration included trickle and hang-on filters, both allowing a more natural equilibrium in the aquarium environment. The advancement of fluorescent lighting technologies to provide higher output, along with metal halide lighting, enabled the first reef tanks, making it possible to keep corals and other invertebrates without natural sunlight. More efficient chemical testing allowed aquarists to understand the chemical properties of aquariums. By the 1980s, a biologically-based understanding of how to maintain an artificial ocean environment brought more successful and widespread marine fishkeeping. Modern fishkeeping Marine aquarium components The major components are an aquarium, usually made from glass or acrylic, filtration equipment, lighting, and an aquarium heater. Marine aquariums can range in volume from less than 80 litres, (< 20 US gal) to over 1,200 litres (300 US gal). Small volumes are more difficult to maintain due to the more rapid changes in water chemistry. The majority of saltwater aquariums are between 160 and 400 litres (40 and 100 US gal). Types of marine aquariums Marine aquarists typically divide saltwater aquariums into those housing fish only, those housing fish with live rock, and those primarily designed to house corals and other invertebrates (also known as reef aquariums). Many fish hobbyists also divide the types of saltwater tanks based on the water temperatures at which they are kept. Tropical marine The most common type of saltwater fish tank, the tropical marine tank, houses marine animals from tropical climates. Usually kept between , these tanks include tropical reef tanks, as well as fish-only tanks. These tanks tend to have a low concentration of microscopic plankton and other foods eaten by filter feeders. Most livestock for these aquariums are acquired through commercial means. Temperate marine (coldwater marine) One of the more obscure types of fish tanks, the coldwater marine tank, holds fish of temperate climates, with temperatures ranging around . Colorful species such as the ornate cowfish, blennies, and sea anemones can be found. The anemones and invertebrates in temperate waters easily rival their tropical counterparts. Most colorful species are found in the western Pacific and west coast of North America. Maintenance of these tanks is similar to keeping a fish only tank with live rock, or a non-photosynthetic tropical aquarium. A significant diversity of species exists. Since coldwater