How Many Fish in a 20 Gallon Tank?
There's no single magic number, a 20-gallon tank can hold a big school of small fish or just a couple of large, messy ones. What matters is each species' adult size, bioload, schooling needs, and temperament. The calculator below is pre-set to 20 gallons; add the fish you're considering and it'll flag any problems.
Example 20-gallon stocking ideas
- Classic community: 8 neon tetras + 6 bronze corydoras + 1 dwarf gourami.
- Livebearer tank: 6 platies or guppies + 6 corydoras.
- Centerpiece + school: 1 honey gourami + 10 harlequin rasboras + amano shrimp.
Always cycle the tank first, add fish gradually, and keep up with weekly water changes. These are starting points, run your exact list through the calculator above.
Fish featured in these 20-gallon setups
Photos via Wikimedia Commons under their respective licenses, click a credit for the source.