A 5 gallon (19 litre) tank gives you fewer options than a 10 gallon, but it can still work for the right species. The key constraint at this size is bioload and fish size — there's very little room for error. Here's what actually works.
Best fish for a 5 gallon tank
| Species | Adult Size | How Many | Why it works |
|---|---|---|---|
| Betta Fish (male) | 6–8 cm | 1 only | The best fish for a 5 gallon. Single male, well-planted. |
| Cherry Shrimp | 2.5 cm | 10–15 colony | Shrimp-only is the most rewarding 5g setup. |
| Nerite Snail | 2.5 cm | 1–2 | Algae control. Can't breed in freshwater. |
Fish to avoid in a 5 gallon tank
| Fish | Why not |
|---|---|
| Any fish other than a betta | 5 gallons is too small for schooling fish — they need groups and swimming room. |
| Corydoras (any species) | Even pygmy corydoras need a group of 6+, which is too crowded in 5 gallons. |
| Tetras or rasboras | Schooling fish need more water volume. 5 gallons cannot support a proper school. |
Stocking plans for 5 gallons
These are combinations I'd actually run in a 5 gallon tank. Each respects bioload, swimming space, and compatibility:
Plan 1: Peaceful Community
Focus on micro-fish and invertebrates. Every fish in this tank should stay under 2 inches as an adult.
Plan 2: Species-Only Display
A shrimp-only or snail-only tank. Invertebrates are the most rewarding inhabitants at this size.
Plan 3: The Biotope
Focus on one biotope with micro-fish from the same region — Southeast Asian blackwater with chili rasboras and boraras species.
Setup tips for a 5 gallon tank
Filtration: A hang-on-back filter rated for 1.5× your tank volume, or a canister filter for 40+ gallon tanks. Sponge filters work for smaller setups.
Heater: 50W for up to 15 gallon, 100W for 20–29 gallon, 200W for 40–55 gallon, 300W for 75+ gallon.
Substrate: For planted tanks, use organic soil capped with sand (Walstad method). For fish-only tanks, use sand or smooth gravel.
Lighting: LED light rated for your tank size. For planted tanks, aim for 1–2 watts per gallon (or the LED equivalent). Avoid overly bright lights — fish feel exposed and will hide.
A 5 gallon is really only suitable for a single betta or a shrimp colony. Don't try to put schooling fish in here.
Before adding any fish, cycle your tank. Use the tank calculator to check your actual water volume, and the stocking calculator to verify your chosen combination fits the bioload.
Frequently Asked Questions
How many fish can I put in a 5 gallon tank?
It depends on the adult size and bioload of the fish. Use the stocking calculator to check your specific combination. As a rough guide, a 5 gallon tank can hold 15-20 small nano fish (under 2 inches) or 6-8 mid-size community fish.
What fish should I avoid in a 5 gallon tank?
See the 'Fish to avoid' table above. The main rule: don't stock fish that will outgrow the tank, and don't put fast swimmers in a tank that's too short for them to swim properly.
Do I need a special filter for a 5 gallon tank?
A sponge filter or small HOB rated for 10-20 gallons is fine.