The short answer
A 50 litre tank is a small community — enough for two little groups on different levels, not a busy mixed tank. A balanced plan is a school of 8–10 nano tetras or rasboras up top plus a group of 6 pygmy corydoras below, with shrimp or a snail as cleanup. Keep the species list short and stock gradually.
Stock by needs, not a number
The “inch of fish per gallon” rule is unreliable because it ignores adult size, bioload, schooling needs, temperament and filtration. Fifty litres is more forgiving than a true nano, but it is still small enough that overstocking quickly shows up as algae, cloudy water and stressed fish. Plan around each species’ real requirements.
Sensible 50 litre stocking ideas
- 8–10 harlequin rasboras + 6 pygmy corydoras
- A honey gourami pair with a nano tetra school
- 6–8 platies as a livebearer tank with shrimp
- 1 betta with a peaceful shoal and a snail crew
Avoid fish that grow large or need long swimming lanes (angelfish, bigger barbs, most cichlids). Schooling fish should always be kept in groups of six or more. A single well-chosen shoal with real numbers beats several thin, stressed groups every time, so resist the urge to add “just one more” species.
Before you add anything
Always cycle the tank first, then add fish a few at a time over several weeks so the filter keeps pace. Keep up weekly water changes and acclimate new fish slowly. For the next step up, see how many fish in a 75 litre tank, and browse the best 60 litre aquariums.