The Cleanest Fish to Put in a 20-Gallon Fish Tank

An aquarium tank that looks sparkling clean could still be holding harmful waste. Fish produce ammonia, which is broken down by bacteria in the tank into less-harmful nitrogen byproducts. Both ammonia and its byproducts are dangerous to fish in high concentrations. Selecting smaller fish that do not produce a lot of waste is one key to a healthy aquarium, as is avoiding tank overcrowding. One rule of thumb is to allow a gallon of tank capacity to an inch of fish. And look for other types of fish besides goldfish: they are popular, but produce a lot of waste.

  1. Barbs

    • One suitable variety is the tiger barb, which is silvery gold with black stripes and a reddish tinge to its fins. Fish breeders have also created albino and green varieties. Tiger barbs are schooling fish that will nip the fins of other fish in the tank. Cherry barbs are less aggressive. The males are a deep red, while the females are reddish-yellow. Six tiger barbs or 10 cherry barbs could live in a 20-gallon tank.

    Danios

    • Zebra danios or zebrafish are silvery-blue with horizontal stripes. A spotted variety is called the leopard danio, and pearl danios are a solid silvery-white color. All three types grow to no more than about 2 inches long. Giant danios get their name because, unlike the other danio types, they can grow to about 6 inches. All danios are fast-swimming fish that enjoy living in schools. Six to 10 of the smaller danios, or three to four giant danios, could live in a 20-gallon aquarium.

    Livebearers

    • Guppies, mollies and swordtails are known as livebearers because the eggs are held inside the female until they hatch. Livebearers prefer to live in water that has some salt in it, about 1 tbsp. for every 5 gallons. This requirement means that other types of fish may not do well in the same tank as livebearers. Remember to leave enough growing room for any offspring that are born in the tank.

    Tetras

    • Dozens of tetra species are available for home aquariums. Like danios, they prefer to be kept with other fish of their kind. Some types that are suitable for a 20-gallon tank include neon tetras, which are streaked with iridescent blue and red; lemon tetras, which have pale yellow bodies and red eyes; black neon tetras, which have a horizontal black-and-silver stripe; and the glowlight tetra, which has a stripe of iridescent orange. These particular tetras grow to no more than 2 inches long.