Tank Size Guide — Finding the Right Fish
for Your Aquarium
From 5-liter pico tanks to 500-liter showpiece aquariums — complete stocking recommendations, equipment lists, and expert tips for every tank size.
5L
— Pico TankSolo Betta OR shrimp-only colony (10 shrimp)
- 1 Betta (solo only)
- OR 10 Cherry Shrimp colony
- 25W heater
- Nano sponge filter
- Clip-on LED light
Goldfish, community tanks, multiple fish species
10L
— Small NanoBetta solo, Chili Rasbora school, shrimp colony
- 1 Betta (solo)
- OR 6 Chili Rasbora + 5 Cherry Shrimp
- OR 15 Cherry Shrimp colony
- Small internal or sponge filter
- 50W heater
- Nano LED light
Goldfish, loaches, angelfish
20L
— Compact CommunityNano community, shrimp + small fish, breeding projects
- 8 Neon Tetra + 5 Cherry Shrimp
- OR 8 Ember Tetra + Otocinclus × 2
- OR 6 Endler Guppy + Otocinclus × 2
- Small HOB filter 100–200 L/h
- 50W heater
- Planted LED 20–30 cm
Clown Loach, Angelfish, Oscar
40L
— Standard BeginnerMost beginner fish, small community, first real tank
- 8 Neon Tetra + 4 Corydoras + 1 Honey Gourami
- OR Guppy colony × 10+
- OR 6 Platy + 4 Corydoras
- HOB filter 200–300 L/h
- 100W heater
- LED 30 cm+ light bar
Koi, Arowana, Clown Loach (long-term)
60L
— Comfortable CommunityProper community, planted tank, cichlid pair
- 10 Cardinal Tetra + 6 Corydoras + 2 Dwarf Gourami + 1 Bristlenose Pleco
- OR German Blue Ram pair + 10 Rummy Nose Tetra + 5 Corydoras
- HOB 300–400 L/h or small canister
- 100–150W heater
- Quality LED or T5 for plants
Discus, large cichlids, Koi
100L
— Serious HobbyistDiscus (min 6), Angelfish group, Rainbow Fish school, biotope
- 6 Discus + 20 Cardinal Tetra + 6 Corydoras Sterbai
- OR 4 Angelfish + 15 Rummy Nose + 6 Corydoras
- OR 10 Boesemani Rainbow + 6 Cory
- Canister filter 500–700 L/h
- 200W heater
- Quality LED or T5 full-spectrum
Full-size Arowana, Koi
200L
— Advanced SpeciesOscar, large cichlids, Arowana (temporary), Clown Loach group
- 2 Oscar + 2 Jack Dempsey (monster tank)
- OR 6 Clown Loach + Angelfish group
- OR 1 juvenile Arowana + carefully chosen tankmates
- Large canister 1000 L/h
- 300W heater
- High-output LED or 2× T5
Multiple large Arowana (highly territorial)
500L+
— Showpiece / ArowanaAsian Arowana, monster fish, predator species, display tanks
- 1 Asian Arowana (solo or very carefully chosen companions)
- OR Large Stingray
- OR Mixed monster predator biotope
- Dual canister filtration system
- Temperature controller + chiller
- Heavy-duty LED bars or metal halide
- Auto top-off / water change system
Small tetras or shrimp (will be eaten), overcrowding
Quick Reference Table
All tank sizes at a glance — compare difficulty, max stocking, and suitability.
| Tank Size | Best Fish | Max Stocking | Difficulty | Notes |
|---|---|---|---|---|
| 5L | Betta solo / Cherry Shrimp | 1 Betta OR 10 shrimp | Intermediate | Very unstable; frequent water changes needed |
| 10L | Betta, Chili Rasbora, Shrimp | 6 nano fish OR 15 shrimp | Beginner+ | Add live plants for stability |
| 20L | Neon Tetra, Ember Tetra, Endler | 8–10 small fish | Beginner | Great breeding / grow-out tank |
| 40L | Tetra, Guppy, Corydoras, Gourami | 12–15 community fish | Beginner | Most forgiving size for beginners |
| 60L | Cardinal Tetra, Dwarf Gourami, Pleco | 15–20 community fish | Beginner | Ideal planted community tank |
| 100L | Discus, Angelfish, Rainbow Fish | 20–30 fish (mixed) | Intermediate | Serious biotope / display potential |
| 200L | Oscar, Clown Loach, Cichlids | 4–8 large fish | Intermediate | Heavy filtration essential |
| 500L+ | Asian Arowana, Stingray, Monster fish | 1–3 large predators | Advanced | CITES rules apply for Arowana |
Common Stocking Mistakes
Avoid these errors to keep your fish healthy and your tank stable from day one.
Overstocking on Day One
Adding 20 fish to a brand-new tank causes ammonia spikes before beneficial bacteria establish. Cycle first, then add fish gradually over 4–6 weeks.
Buying Fish That Outgrow the Tank
A Common Pleco sold at 5 cm grows to 45+ cm. An Oscar sold as a "cute orange fish" becomes a 35 cm waste machine. Research adult size, not store size.
Ignoring the "1 Inch Per Gallon" Myth
This outdated rule ignores fish body shape, activity level, and waste production. A 30 cm Goldfish is not the same as 30 cm of Neon Tetras.
Mixing Incompatible Species
Bettas will kill fancy guppies. Cichlids will terrorize peaceful community fish. Always research temperament, water parameter overlap, and territorial behaviour before mixing.
Skipping the Nitrogen Cycle
An uncycled tank has zero beneficial bacteria. Fish waste becomes toxic ammonia within hours. Fishless-cycle your tank for 2–4 weeks before adding any livestock.
Undersized Filtration
A filter rated for your exact tank volume is already undersized. Target 4–6× tank volume per hour for community tanks, 8–10× for messy species like Oscar or Discus.
Ready to Stock Your Tank?
Browse our full collection of fish, shrimp, equipment, and plants — matched to every tank size in this guide.