What can you keep in a 20 US-gallon tank?

Plans worth checking on their own

Each idea is a separate plan, not a list to combine. Check the species and the numbers in the tank builder before you buy.

• Harlequins and corydoras

  Six or more harlequin rasboras with six corydoras on sand. Corydoras use the floor. Aqueon's published outer length is 61.6 cm on the 20 High and 76.8 cm on the 20 Long, so measure the inside before you treat either as a 60 cm run. The rasboras stay in midwater and the corydoras on the sand.

• A neon school

  Eight to ten neon tetras. A 20-gallon tank is large enough on volume. Seriously Fish asks for a 60 × 30 cm base. Aqueon's outer bases are 61.6 × 31.8 cm and 76.8 × 31.8 cm, only slightly larger than that, and those are outside measurements. Measure the inside before you rely on that base. Neons do best in soft water, about pH 6–7.

• Platies in hard water

  Three or more platies in hard water, about pH 7–8. Keep soft-water fish such as neons out of this plan.

Other species need a closer look

These meet the volume minimum too, but fall outside the shortlist above because of their care needs, size or behaviour. A volume match does not make them suitable tank mates.

Species that need a larger tank

A 20-gallon tank is too small for mollies, swordtails, bristlenose plecos, tiger barbs, German blue rams, peppered corydoras and zebra danios.

Each of these needs a larger tank than 20 US gallons. Buying a small juvenile does not change that.

• Adolfoi cory →

  Needs a larger tank than 20 US gallons.

  Planning minimum 80 litres (21.14 US gal).

• Agassiz’s dwarf cichlid →

  Needs a larger tank than 20 US gallons.

  Planning minimum 80 litres (21.14 US gal).

• Apistogramma Borellii →

  Needs a larger tank than 20 US gallons.

  Planning minimum 80 litres (21.14 US gal).

• Apistogramma Trifasciata →

  Needs a larger tank than 20 US gallons.

  Planning minimum 80 litres (21.14 US gal).

• Bamboo Shrimp →

  Needs a larger tank than 20 US gallons.

  Planning minimum 80 litres (21.14 US gal).

• Black phantom tetra →

  Needs a larger tank than 20 US gallons.

  Planning minimum 80 litres (21.14 US gal).

• Bristlenose Pleco →

  Needs a larger tank than 20 US gallons.

  Planning minimum 80 litres (21.14 US gal).

• Celebes Rainbowfish →

  Needs a larger tank than 20 US gallons.

  Planning minimum 80 litres (21.14 US gal).

• Chocolate gourami →

  Needs a larger tank than 20 US gallons.

  Planning minimum 80 litres (21.14 US gal).

Common mistakes at this size

• Choosing zebra danios for a 20-gallon tank. They need a larger tank, and Seriously Fish asks for a base of about 90 × 30 cm. The 20 High's published outer length is 61.6 cm.
• Assuming a 20 High and a 20 Long suit the same fish. They hold the same water. The 20 Long's published outer length is about 15 cm more, and the 20 High is about 10 cm taller.