Choosing fish wisely begins with research and a healthy skepticism toward the old rule of one inch of fish per gallon. That guideline ignores differences in bioload, the amount of biological waste each species produces, as well as behavior and territory needs. Every potential species should be evaluated for adult size, temperament, schooling requirements, dietary preferences, and water parameters. Schooling fish such as neon tetras, cardinal tetras, rummynose tetras, and harlequin rasboras must be kept in groups of at least six to feel secure and display natural behavior. Livebearers like guppies, platies, mollies, and swordtails give birth to free-swimming young, and keeping two to three females per male reduces harassment of any single fish.
Popular community fish include tetras, rasboras, danios, some gouramis, corydoras catfish, and livebearers. Larger or more striking centerpiece fish might be angelfish, dwarf gouramis, pearl gouramis, or German blue rams. Bottom dwellers such as corydoras, kuhli loaches, and otocinclus round out the tank by occupying the substrate. Plecos are a special case: the common pleco grows to 18 to 24 inches and needs an enormous tank, while the bristlenose pleco stays around five inches and is a much better choice for most home aquariums. Bettas are usually kept one male per tank because they will fight, though female bettas can sometimes be housed in groups of five or more in larger, well-structured sororities.
Feeding should be done two to three times daily in small amounts that fish consume within a couple of minutes, and the rule of underfeeding rather than overfeeding protects water quality. A varied diet of flakes, pellets, frozen, freeze-dried, and occasional live or vegetable foods mimics natural nutrition. New arrivals must be acclimated slowly, ideally by dripping tank water into the transport bag over 30 to 60 minutes, so they adjust to both temperature and chemistry. Quarantining new fish for about 30 days in a separate tank is one of the most effective ways to prevent disease outbreaks in the main display.