The short answer
For a 20 litre (about 5 gallon) tank, start with 10–15 cherry shrimp and let the colony grow on its own. Shrimp have a very small bioload, so a mature 20 litre tank can happily support 50 or more over time — but you rarely need to add that many, because a healthy colony breeds and self-regulates to the space and food available. A dedicated shrimp tank is one of the best uses of a nano.
Why shrimp are different from fish
The old “inch of fish per gallon” rule does not apply to shrimp at all. What matters is bioload (tiny), stable water parameters and a mature, biofilm-rich tank for them to graze. Because each shrimp produces so little waste, stocking is far more relaxed than with fish — the real limits are food supply and how stable you keep the water, not raw numbers.
Stocking shrimp well in 20 litres
- 10–15 cherry shrimp to start, then let them breed
- Add plenty of plants, moss and biofilm for grazing and cover
- Keep a few snails as tankmates; skip fish, which eat shrimplets
- Amano shrimp are an option too, but they don’t breed in freshwater, so numbers stay fixed
Avoid copper-based medications and sudden parameter swings — shrimp are sensitive to both.
Before you add anything
A shrimp colony needs a stable, established tank, so cycle it fully and ideally let it mature before adding your starter group. Acclimate them very slowly and keep up gentle weekly water changes. For fish options at this size, see how many fish in a 20 litre tank, and for the tank itself browse the best nano aquariums.