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.