Quick Stats
| Adult Size | 2 cm |
| Minimum Tank | 5 gal |
| Temperature | 20–28°C |
| pH Range | 4.0–7.0 |
| Hardness (GH) | 1–5 dGH |
| Difficulty | Easy |
| Temperament | Peaceful, tight-schooling |
| Diet | Omnivore — micro pellets, crushed flakes, baby brine shrimp, vinegar eels |
| Schooling | 8–10+ required |
Tank Setup
The Chili Rasbora (Boraras brigittae) is a deep red micro-rasbora from the peat swamps of Borneo, and it is one of the most rewarding nano fish you can keep — provided you commit to the water it evolved in. A 5 gallon tank is the floor for a species-only school of 8–10, but a 10 gallon gives you room to add Pygmy Corydoras or shrimp as a cleanup crew. Anything smaller than 5 gallons is too volatile for a fish this small.
Maintain water parameters within: temperature 20–28°C, pH 4.0–7.0, hardness 1–5 dGH. That pH range is not a suggestion — it is the difference between a glowing red fish and a translucent grey one. Straight tap water in most cities is pH 7.5–8.2 and GH 8–15, which will slowly kill Chili Rasboras over weeks. I run my chili tank at 26°C, pH 5.2, GH 2, mixing 80% reverse osmosis water with 20% tap water and filtering through peat. Indian almond leaves and alder cones drop the pH naturally and tint the water the colour of weak tea.
Set up the tank with dark sand, driftwood, dense planting, and leaf litter. Floating plants (Salvinia, frogbit) dim the light and recreate the shaded forest pools they come from. A sponge filter is plenty — they cannot fight any current and a hang-on-back filter's return flow will pin them against the far glass. Avoid bare-bottom tanks and bright lights; both wash out the red and stress the school.
Tank Mates
Chili Rasboras are tiny, peaceful, and completely defenceless — which means the list of compatible tank mates is short. Anything with a mouth large enough to swallow a 2 cm fish is a predator, and anything boisterous enough to outcompete them at feeding time will starve them slowly.
Compatible tank mates include: other Chili Rasboras (mandatory — they school), Ember Tetras, Celestial Pearl Danios, other Boraras species (Phoenix, Mosquito, Least), Pygmy Corydoras, Otocinclus, sparkling gourami (in a 15 gallon or larger), Cherry Shrimp, and Nerite Snails. They also work with a single Betta in a 10 gallon or larger, provided the betta is on the peaceful side. Avoid guppies, platies, swordtails (wrong water), danios (too fast, too big), and any cichlid.
Schooling is non-negotiable. Eight is the absolute floor; ten to fifteen is what I aim for. A group smaller than eight will hide constantly, lose their red, and slowly fade — both in colour and in health. In a proper school of fifteen, the males flash deep crimson at each other and the whole group moves as a tight orange-red ribbon through the plants.
Diet & Feeding
Chili Rasboras are micro-predators in the wild, eating tiny crustaceans, insect larvae, and zooplankton. In the aquarium they accept micro pellets, crushed flakes, frozen daphnia, frozen cyclops, vinegar eels, and live or frozen baby brine shrimp. The key constraint is mouth size — they cannot eat anything bigger than about 0.5 mm, so standard tropical flakes are useless without crushing.
Feed small amounts twice daily. Crush flakes to a fine powder between your fingers before dropping them in, or use a dedicated micro pellet (I use New Life Spectrum Nano and Bug Bites Tropical Small Granules). Live baby brine shrimp twice a week deepens the red noticeably within a week — it is the single best colour food I have found for this species. Skip dry-only diets; the red will drift toward pink within a month.
They are surface and mid-water feeders, so floating or slow-sinking foods work best. They will not compete with bottom feeders for sunken food, and they cannot outcompete Ember Tetras or CPDs at the surface — if you mix species, target-feed the chilis with a baster or pipette into a calm corner. They will pick at biofilm and infusoria in a mature planted tank, which supplements the diet between feedings.
Common Health Issues
Chili Rasboras are hardy once acclimated to proper water — but they are unforgiving of poor water chemistry. The single biggest issue I see is pale, hiding fish in hard alkaline tap water. A chili rasbora in pH 7.8, GH 12 will lose its red within two weeks, refuse food within a month, and die of secondary infections within two months. This is not a fish for untreated tap water.
Like all tetras and rasboras they are susceptible to ich when stressed by temperature swings or ammonia spikes. The standard heat-and-salt treatment works, but raise temperature slowly (1°C per day) and stop at 28°C — pushing to 30°C will stress them more than the ich itself. Copper medications are toxic at standard doses for fish this small; dose at 50% of label rate or use malachite green-free alternatives. Quarantine every new fish for two weeks before adding it to a chili tank.
Prevention is straightforward: stable soft acidic water, weekly 20% water changes with matching-chemistry water (not cold tap), and a mature biofilter. They typically live 3–5 years in good conditions, with the upper end coming from cooler tanks (24–26°C) and stable parameters. A chili tank that has been running for six months is far easier to keep than a new one — let the biofilm and infusoria build up before adding the school.
Breeding
Chili Rasboras are egg-scatterers and breed readily in soft acidic water. Sexing is straightforward: females are rounder and slightly larger with a yellowish body, males are slimmer and a deeper, more saturated red. Condition a group with live baby brine shrimp and frozen daphnia for a week, then move them to a 5 gallon spawning tank at 27°C, pH 5.0–5.5, with a spawning mop or dense Java moss.
Spawning happens in the early morning, often triggered by a cool water change the evening before. A female scatters 20–60 adhesive eggs among the plants or mop; the male follows and fertilises them. Remove the adults immediately after — they will eat every egg they can find within hours. The eggs are light-sensitive, so dim the tank or cover it with a towel for the first 24 hours.
Eggs hatch in 24–36 hours. Feed the fry infusoria or commercially-prepared liquid fry food for the first five days — they are too small for anything else, including newly-hatched brine shrimp. Graduate to vinegar eels at day five, then to live baby brine shrimp at day ten. Chili fry grow slowly and are free-swimming within a week, but they take three months to reach the size where they can join the adult school. This is a rewarding breeding project for aquarists already running a blackwater setup.
Frequently Asked Questions
Are Chili Rasboras hard to keep?
Not hard, but unforgiving of tap water. They need soft, acidic water (pH 4.0–6.5, GH 1–5) to thrive — straight out of the tap in most cities is too hard and too alkaline, and they will fade, hide, and slowly die. In a properly set up blackwater tank they are peaceful, hardy, and long-lived.
How many Chili Rasboras should I keep together?
Eight is the absolute minimum; 10–15 is what I aim for. They are a tight-schooling micro-rasbora and a group smaller than eight will hide constantly and lose their red colour. A larger school also makes the males display far more intensely, with the deep crimson that gives the species its name.
Can I keep Chili Rasboras in a 5 gallon tank?
Yes, but only as a species-only tank with 8–10 fish, heavily planted, and with stable water parameters. A 5 gallon is too small to mix with other fish. A 10 gallon is the more forgiving choice and lets you add Pygmy Corydoras or shrimp as a cleanup crew.
Why are my Chili Rasboras not red?
Three usual causes: water is too hard and alkaline (they need pH below 6.5 and GH below 5), the school is too small (under 8 fish go pale from stress), or the tank is too bright with a light substrate. They colour up best in tannin-stained water over dark sand with dim lighting and a proper school.