levels of nitrates, phosphates, and silicates and other dissolved solids which fuel the growth of nuisance algaes, particularly diatoms, which appear as a rust-colored powdery algae and grows in the overabundance of silicates present in all tap water. Water filtered by a four-stage process including mechanical, carbon, reverse-osmosis, and de-ionizing components is recommended as this can provide the easiest route to absolutely pure water. Four- and five-stage RO/DI filtration units can be obtained for as little as $100 and are a cost-effective means of converting tap water into water usable in a marine aquarium. Conservation Almost all species kept in marine aquaria at this time are caught in the wild, although tank-raised specimens are becoming increasingly common as a viable alternative. The list of marine aquarium fish, such as clownfish that are captive-bred and available on a commercial scale, is increasing. As of a 2019 report, there were nearly 400 known captive-bred species, 46 that were considered commonly available. Much collecting is done in Indonesia and the Philippines, where use of cyanide and other destructive collection methods, while discouraged, is unfortunately common. The majority of live rock is also harvested in the wild, and recent restrictions on this harvest in Florida have caused a shift to Fijian and aquacultured rock. Natural rock, because it is created by coral polyps, takes many years if not centuries to form, and is a vital habitat for countless marine species; thus, commercial-scale harvesting of naturally occurring live rock has been criticized by conservationists. Additionally, many animal species sold to hobbyists have very specific dietary and habitat requirements that cannot be met by hobbyists (e.g. genus Labroides wrasses, the moorish idol); these animals almost inevitably die quickly and have markedly reduced lifespans compared to wild specimens. Often these specific environmental requirements cause improperly housed livestock's color and appearance to be poor. These issues are often downplayed by individuals and organizations with a financial interest in the trade. Hobbyists who support conservation should buy only certified net-caught fish (although ensuring the legitimacy of such claims can be difficult) or captive-raised fish, as well as farmed corals and to support legitimate reef conservation efforts. The majority of corals can be "fragged", whereby a portion of a larger captive coral is separated and can subsequently be raised into an individual specimen, allowing for coral propagation within the domestic aquarium; the trade in frags (i.e. fragments) offers a fantastic