15 Best Small Tropical Fish for Nano Tanks

The best small tropical fish for nano tanks share a few important traits: they stay under 5 cm as adults, they are active enough to be interesting in a small space, they do not produce excessive waste, and they tolerate the slightly less stable water parameters that come with smaller water volumes.

Most of the fish on this list are schooling species — they need groups of at least six to feel secure and show their best colours. A 30-litre nano tank can comfortably hold a school of one small species. A 60-litre tank gives you room to mix two compatible groups.

The golden rule of nano fishkeeping: understocking is always better than overstocking. In a small tank, every extra fish matters.

At just 1.5–2 cm, the Chili Rasbora is the crown jewel of nano fishkeeping. Males glow a deep ruby red that intensifies in soft, slightly acidic water with dark substrate and plenty of plants. They are peaceful, active, and endlessly watchable as they dart through plant stems in a tight little school.

Keep them in groups of eight or more — the larger the group, the bolder they become and the better the males colour up. They eat micro pellets, crushed flakes, and live baby brine shrimp. Perfect for a 20-litre planted nano tank.

Also called the Galaxy Rasbora, this tiny fish looks like someone painted stars on its body. Deep blue-black flanks covered in pearlescent gold spots, with vivid orange-red fins — the Celestial Pearl Danio is one of the most beautiful freshwater fish on the planet, and it only grows to 2.5 cm.

They prefer cooler tropical temperatures (20–24 °C) and planted tanks with plenty of cover. Males spar gently for territory, fanning their fins in display — it is one of the most entertaining behaviours in nano fishkeeping. Keep at least six, with more females than males to reduce competition.

The Ember Tetra is a warm, fiery orange that glows under aquarium lighting. At 2 cm, they are one of the smallest tetras available, and they school beautifully in planted tanks. A group of ten Ember Tetras in a densely planted 40-litre tank is one of the most visually striking setups in the hobby.

They are hardy, peaceful, and do well with cherry shrimp — making them perfect for a shrimp-and-fish community nano tank. Feed them crushed flakes and the occasional frozen daphnia for best colour.

Most corydoras are bottom dwellers, but the Pygmy Cory breaks the rules. These 2-cm micro catfish hover in the mid-water, perching on plant leaves and darting around in groups. They are sociable, peaceful, and endlessly entertaining — like tiny silver helicopters patrolling your tank.

Keep them in groups of eight or more on fine sand substrate. They mix brilliantly with other nano species like Ember Tetras and Chili Rasboras. One of the best small tropical fish for anyone who wants activity at every level of their tank.

Beyond our top picks, here are ten more excellent small tropical fish for nano and small tanks:

• Neon Tetra (3 cm) — the classic. Iridescent blue and red in schools of six or more. Shop tetras
• Green Neon Tetra (2.5 cm) — smaller and more intensely coloured than regular neons
• Endler's Livebearer (2.5 cm) — tiny, colourful livebearers that breed readily
• Sparkling Gourami (3.5 cm) — actually makes audible clicking sounds. Fascinating micro predator
• Scarlet Badis (2 cm) — jewel-coloured micro predator for experienced keepers
• Least Killifish (2.5 cm) — one of the smallest livebearers in the world
• Exclamation Point Rasbora (2 cm) — named for the marking on its body. Tiny and peaceful
• Phoenix Rasbora (2 cm) — vibrant orange-red, similar to Chilis but slightly different colouring
• Dwarf Pencilfish (3 cm) — elegant, torpedo-shaped surface dwellers
• Asian Stone Catfish (3 cm) — bizarre, rock-mimicking bottom dweller for planted tanks

All of these stay under 4 cm and work well in tanks from 30 litres upward. Combine them with freshwater shrimp and nerite snails for a complete nano ecosystem.

Not sure how to combine these fish? Here are three proven stocking plans:

30-litre planted nano:

• 8x Chili Rasboras + 5x Cherry Shrimp + 2x Nerite Snails

60-litre community nano:

• 8x Ember Tetras + 6x Pygmy Corydoras + 10x Cherry Shrimp

80-litre colourful nano:

• 10x Celestial Pearl Danios + 8x Chili Rasboras + 6x Pygmy Corydoras

In every case, add fish in stages over several weeks and test your water parameters before each addition. Read our complete tank setup guide if you are starting from scratch.