Types of Saltwater Aquariums

Since not all saltwater species coexist happily in an aquarium environment, saltwater aquariums are categorized into several different types of systems based on the species living in the tank and how much care they need. While all saltwater aquariums require light, filtration and proper water quality, different types of systems have different requirements and different margins of error. The organisms inhabiting the aquarium determine lighting, filtration and water quality parameters.

  1. Fish Only

    • The blueline triggerfish is a hardy and colorful fish-only specimen.

      Fish-only tanks are the simplest type of saltwater aquarium to set up and easiest to maintain. They require minimal lighting (1 watt per gallon) and can be aqua-scaped with artificial decorations. According to "The Conscientious Marine Aquarist" by Robert Fenner, since fish-only tanks typically showcase large, hardy fish species, "the worries and expenses of maintaining optimum water quality are greatly diminished." The biggest concern is filtration since saltwater fish are heavy waste producers and fish-only tanks typically do not have sources of natural filtration (such as live rock or detritus-eating hermit crabs). Aggressive saltwater species that are prone to eating smaller fish and invertebrates and damaging corals are best kept in fish-only tanks. Examples of suitable fish-only species include puffers, groupers, lionfishes and eels. Always check to ensure species are compatible before introducing them into the tank together and never crowd aggressive species.

    FOWLRs

    • Cardinalfishes are a good choice for FOWLR tanks because they typically do not eat invertebrates.

      Fish-only-with-live-rock tanks are known as "FOWLRs." The main difference between fish-only saltwater tanks and FOWLRs is the inclusion of invertebrates, which require additional lighting (3 to 4 watts per gallon) and more frequent water quality testing. Many invertebrates require not only more lighting but also a regular lighting schedule, which in most cases also requires the addition of a light timer. Invertebrates cannot tolerate fluctuating water quality and most cannot tolerate the presence of metals in the water. Since invertebrates are more delicate, the saltwater fish species kept in FOWLRs should not be as aggressive as fish-only stock. Examples of suitable invertebrates for FOWLR tanks include starfish, crabs, shrimps, anemones and feather duster worms. Suitable fish for FOWLR systems could include clownfishes, cardinalfishes, damselfishes and firefishes.

    Reef

    • This reef tank includes acropora, zooanthids, lobophyllia, platygyra and a colorful anthias reef fish.

      Reef tanks are the most difficult type of saltwater aquarium systems to maintain. Reef tanks include delicate corals in addition to fish and invertebrate species. Water parameters must be meticulously maintained for success with a reef tank. Because of the symbiotic algae living in the tissue of coral species, reef tanks require high lighting and thoughtful placement of the corals. As a basic rule of thumb, the more lighting a reef tank has, the more delicate coral species can be kept. Compact fluorescent lights work well for beginner reef tanks and metal halide lighting is the common choice among advanced reef keepers. Another requirement for reef tank systems is strong circulation via the inclusion of pumps. As Fenner points out, most saltwater reef aquarium setups "represent thousands of dollars of investment, and their keepers often spend hundreds more per month" on upkeep. According to Julian Sprung's reference guide to corals, hardy coral species suitable for beginning reef keepers include leather corals, mushrooms, zooanthids and cynarina. More delicate coral species include acropora, physogyra and eupyhllia.