Chili Rasbora Care Guide: Tank Size, Diet & Tank Mates for Boraras brigittae

Species Overview#

Chili rasboras (Boraras brigittae) are one of the smallest schooling fish in the freshwater hobby — adults rarely break 0.8 inches (2 cm), and their bodies glow a saturated crimson red with a sharp black lateral stripe. They come from the tannin-stained peat swamps of southwestern Borneo, where soft, acidic water and a thick canopy of vegetation define their world. Drop a school of 15 into a planted nano tank, and they look like embers drifting through the water column.

They are not difficult to keep, but they are not a "drop them in tap water and forget about it" fish either. Their tiny size, narrow water chemistry preferences, and micro-sized mouths put them in their own category. Read this guide before you buy — every parameter on the list matters more for a 0.8-inch fish than it does for a 3-inch tetra.

Adult size

0.8 in (2 cm)

Lifespan

4-8 years

Min tank

5 gallons

Temperament

Peaceful, shoaling

Difficulty

Beginner with stable parameters

Diet

Micropredator

Natural Habitat#

Boraras brigittae lives in the blackwater peat swamps and slow-moving forest streams of southwestern Borneo, particularly around the Kapuas River basin. The water in these habitats is the color of strong tea — stained by tannins leaching from decaying leaf litter, peat, and submerged wood. Visibility is low, current is almost nonexistent, and the substrate is a dark layer of decomposing plant matter rather than sand or gravel.

The chemistry is extreme by aquarium standards: pH frequently sits between 4.0 and 5.5, total hardness measures near zero, and the water is heavily shaded by overhead jungle canopy. Light reaches the fish in dappled patches, not the open glare of a typical reef-style LED setup. Replicating even a softened version of this environment in your aquarium pays off immediately in coloration and natural behavior.

Appearance & Size#

Males display the classic chili rasbora look — a vivid red body with a black horizontal stripe running from gill to tail base, edged in red where it meets the body. Fins carry red highlights, and dominant males flush a deeper, more uniform crimson when they're displaying or competing for females. Females are slightly larger and rounder in the belly, with paler color and a thinner lateral stripe.

Adult size tops out around 0.8 inches (2 cm). They are sometimes confused with the related Boraras maculatus (dwarf rasbora) and Boraras urophthalmoides (least rasbora), but the solid black lateral stripe and uniform red body are diagnostic for brigittae. The trade name "mosquito rasbora" gets used interchangeably, though that label originally referred to Boraras urophthalmoides.

Lifespan#

Well-kept chili rasboras live 4 to 8 years in the home aquarium. Most losses in the first year come from fish-in cycling, sudden chemistry shifts during water changes, or undetected parasites brought in with new tank mates. Once they settle into a stable, well-cycled tank with appropriate water chemistry, they are remarkably persistent for such a small fish.

Their longevity is tied directly to parameter stability. A tank that swings between pH 6.0 and 7.5 over the course of a few weeks will shorten their lives even if neither value is technically lethal.

Water Parameters & Tank Requirements#

Get the chemistry right before the fish arrive. With a body mass measured in fractions of a gram, chili rasboras have no buffer against ammonia spikes, big temperature swings, or pH crashes. The single most important predictor of success is a fully cycled tank and stable parameters at the time of stocking.

Ideal Water Parameters#

Aim for a temperature of 72-80°F (22-27°C). The often-cited 68-82°F range is technically tolerable, but the lower end slows metabolism and increases ich susceptibility, and the upper end shortens lifespan. Settle on 76°F as a comfortable middle.

Target pH 5.5-7.0 for most home setups, with 6.0-6.5 being the sweet spot for color and breeding behavior. Wild populations live below pH 5.5, but tank-bred specimens — which now dominate the trade — handle the slightly higher range fine. Hardness should sit between 1 and 5 dGH; chili rasboras struggle long-term in hard tap water (8 dGH or above), even when other parameters look good.

If your tap water reads above 7.5 pH or above 8 dGH, blend it with RO water at roughly 50/50 to soften and acidify before water changes. Botanicals (Indian almond leaves, alder cones, oak leaves) gradually lower pH and add the tannins these fish evolved with.

Minimum Tank Size & Stocking#

A 5-gallon tank is the realistic minimum for a small group of 6-8 chili rasboras. They are tiny and they don't move much, but a smaller tank than that gives no margin for parameter swings — a 2.5-gallon "pico" setup is a stress trap, not a home.

A 10-gallon planted tank is the practical sweet spot. It comfortably holds 15-20 chili rasboras with neocaridina shrimp, a small bottom-dweller like pygmy corys, and dense plant cover. The visual payoff of a school that size in a heavily planted tank is what makes this species famous in nano aquascaping circles. The Fluval Flex 9-gallon or 15-gallon is a near-perfect off-the-shelf nano tank for chili rasboras — the curved front, built-in filtration chamber, and mid-range light suit them well with minor modifications.

Dense planting matters as much as raw gallonage. Chili rasboras feel exposed in open tanks and will hover near the back glass; give them a thicket of stem plants, floating cover, and shaded areas and they will school confidently in the open water column.

Filtration & Flow#

A sponge filter is the standard recommendation for chili rasbora tanks, and for good reason. It provides gentle biological filtration without the ripping current of a hang-on-back filter, and the sponge surface is shrimp-fry-safe (no impeller intake to mince invertebrate babies). For a 10-gallon nano with chilis and shrimp, a single sponge filter rated for a 20-gallon tank is appropriate.

If you prefer a hang-on-back or small canister, baffle the output with a sponge prefilter or a flow diffuser. Chili rasboras are weak swimmers — visible drift across the tank from filter return current means the flow is too high. Watch the fish: if they're hovering in one calm corner instead of using the full water column, ease off.

Lighting#

Low to moderate lighting works best. Bright open-tank lighting bleaches their color (the red is camouflage against a dark, dim swamp floor — they tone it down when they feel exposed) and stresses the school into hiding.

Floating plants — red root floaters, dwarf water lettuce, salvinia, frogbit — diffuse light, provide cover, and give the chilis a feeling of canopy overhead. A planted tank with floating cover and tinted water is the visual environment they evolved for, and you'll see it in their behavior within days of dialing it in.

Diet & Feeding#

Chili rasboras are micropredators in the wild, picking off tiny crustaceans, insect larvae, and zooplankton from the water column and leaf litter. Their feeding strategy in the aquarium has to match that mouth size — under half a millimeter at the gape.

What Chili Rasboras Eat#

The best staple foods are small live and frozen items: baby brine shrimp (freshly hatched, not adult), daphnia, micro worms, vinegar eels, and cyclops. These match their natural prey size and trigger active hunting behavior across the tank.

If you can culture micro worms or vinegar eels, do it. A small scoop of either daily turns a sluggish school into an animated one. Frozen daphnia and frozen baby brine are widely sold and store well — keep both in the freezer as backup staples.

Dry Food Options#

Dry food works for chili rasboras, but particle size is the deciding factor. A standard tropical flake or "nano pellet" labeled for tetras is too large — they'll spit it out repeatedly until it dissolves enough to eat, and most of it ends up rotting on the substrate.

Crushed nano pellets (Hikari Micro Pellets, Bug Bites Nano formula, Omega One Micro Pellets) work if you grind them between your fingers to a near-powder before sprinkling. Micro flake products marketed for fry — like Hikari First Bites or NLS Grow — are appropriate adult food for these fish, not just fry food. Aim for particle sizes of 0.5 mm or smaller.

Feeding Frequency & Quantity#

Feed twice daily in small amounts — only what the school can clear within a minute or two. In a low-flow nano tank with limited water volume, overfeeding is the fastest route to ammonia spikes and shrimp die-offs. A pinch of crushed flake or a teaspoon of just-hatched baby brine for a school of 15 is plenty.

If you keep shrimp in the same tank, the shrimp will scavenge anything the rasboras miss, but don't use that as an excuse to dump food. Skip a feeding day every 7-10 days to give their systems a break and let the bioload settle.

Tank Mates & Compatibility#

Chili rasboras need calm, similarly sized tank mates and absolutely no aggression. Their size puts a hard ceiling on what they can safely live with — even a peaceful 3-inch fish like a honey gourami can stress them just by existing in the same water column.

Best Nano Tank Mates#

The proven pairings are other peaceful nano species: ember tetras, pygmy corydoras (Corydoras pygmaeus or C. hastatus), sparkling gouramis, scarlet badis (single male, with caution), and other Boraras species like phoenix rasboras or dwarf rasboras. Otocinclus catfish work well as algae-eating tank mates, but they need a mature tank with established biofilm.

A textbook "nano biotope" tank for chili rasboras is a 10-15 gallon planted aquarium with chilis, pygmy corys on the substrate, neocaridina shrimp throughout, and a clump of floating plants on top. That setup gives every species its own zone and avoids competition.

Invertebrate Compatibility#

Chili rasboras are excellent shrimp tank mates. Adult neocaridina (cherry, blue dream, yellow) and caridina (crystal red, taiwan bee) shrimp are completely safe — the rasboras' mouths are too small to do any damage to a 1-inch adult shrimp. They will occasionally pick off newborn shrimplets, but in a planted tank with moss, almond leaves, and dense ground cover, enough babies survive to maintain the colony.

Snails are also safe partners. Nerite snails, ramshorns, and Malaysian trumpet snails coexist with chili rasboras with zero conflict. If you want a peaceful planted tank with mixed inverts and one fish species, this combination is hard to beat.

Fish to Avoid#

Avoid anything large enough to fit a chili rasbora in its mouth — and that's a long list. Skip angelfish, larger gouramis, dwarf cichlids, livebearers larger than guppies (and even male guppies can outcompete chilis at feeding time), and any catfish over 3 inches. Avoid all known fin-nippers (tiger barbs, serpae tetras) regardless of size. Goldfish and chili rasboras are biologically incompatible — different temperatures, different water chemistry, predator and prey.

If you're unsure whether a species is safe, look up its adult size and feeding behavior in the freshwater fish guide or ask LFS staff. The safe list for nano-fish-only tanks is short, but it's reliable.

Breeding Chili Rasboras#

Breeding chili rasboras at home is achievable for hobbyists who get the water chemistry right and provide proper fry-rearing infrastructure. They spawn readily in dedicated breeding setups, but raising fry requires live food cultures and patience.

Sexing & Conditioning#

Sexing is straightforward in adults. Males are smaller, slimmer, and more intensely colored — a dominant male flushes a saturated red across the entire body. Females are slightly larger, rounder in the belly when egg-laden, and noticeably paler. Both sexes carry the lateral stripe, but it's typically more vivid in males.

Condition the breeders for 1-2 weeks on a varied diet of live baby brine, daphnia, and micro worms. Move conditioned pairs (or a small group of 2 males to 4 females) to a separate breeding tank with mature water, java moss or spawning mops, and dim lighting.

Spawning & Egg Care#

Chili rasboras are egg scatterers. They release eggs into plants and on the substrate with no parental care — and the parents will eat eggs and fry given the opportunity. Trigger spawning with soft, acidic water (pH 5.5-6.0, sub-2 dGH hardness), a slight temperature bump to 78-80°F, and a generous live food regimen.

Remove adults after spawning. Eggs hatch in 24-48 hours, and fry are tiny — too small for newly hatched baby brine for the first 5-7 days. Start fry on infusoria, paramecium cultures, or commercial liquid fry food (Sera Micron, Hikari First Bites at the smallest particle size). Switch to baby brine once they're large enough to handle it. Expect a slow grow-out — fry take 3-4 months to reach saleable size.

Common Health Issues#

Chili rasboras are not particularly disease-prone, but their tiny body mass means treatments and stressors hit harder than they would on a larger fish. Prevention through water quality and quarantine is more effective than reactive treatment.

Ich & Velvet#

Ich (Ichthyophthirius multifiliis) presents as small white spots on the body and fins. It's most common at the lower end of the temperature range (below 74°F) and after stressful events like shipping or new tank introductions. Treat by raising the temperature to 82°F gradually and using an ich-specific medication at the lowest effective dose — chili rasboras are sensitive to copper and full-strength malachite green.

Velvet (Piscinoodinium) is harder to spot — a fine gold or rust-colored dust on the body, often visible only in side-lighting. It progresses faster than ich and can wipe out a school in a few days. Treatment is more delicate; consult a fish-disease guide for low-dose copper or formalin protocols, and dose for the actual tank volume, not the labeled "average tank size."

Bacterial Infections & Stress#

Bacterial infections in chili rasboras almost always trace back to water quality. Cloudy eyes, fin rot, or sudden lethargy in one fish in a stable group usually means a parameter has slipped — test ammonia, nitrite, nitrate, and pH first before reaching for medication. A water change with parameter-matched water often resolves early-stage symptoms without antibiotics.

Where to Buy & What to Look For#

Chili rasboras are widely available in the trade — most major US online vendors carry them, and any local fish store with a serious freshwater section should have them or be able to order them. Where you buy matters less than how the fish were handled in the supply chain.

Finding Healthy Chili Rasboras at Your Local Fish Store#

Look for active shoaling behavior. A healthy chili rasbora school stays together in the open water column or hovers as a group near plants — not scattered individuals hugging corners or hanging at the surface. Coloration should be vivid red on at least the dominant fish; faded, washed-out fish typically indicate stress or recent shipping arrival.

Check for clamped fins, white spots, fungal patches, or any "fuzzy" outline along the body. A school of 20 in a store tank should have zero visible disease — if you see one obviously sick fish, the whole batch is at risk. Ask staff how long the fish have been in-store; ideally they've been settled for at least a week, and the staff should be feeding them visibly during your visit.

Online vs. LFS Sourcing#

Local fish stores let you inspect the fish in person, watch them eat, and ask about source — captive-bred (most stock these days) vs. wild-caught. Captive-bred specimens adapt to standard tap water more readily and arrive less stressed than wild-caught fish that may have crossed multiple borders.

Online sourcing offers wider color and sourcing options but adds shipping stress. If you order online, schedule arrival for a midweek delivery (avoid Friday-Saturday delivery windows where the fish may sit overnight in a sorting facility), and have your quarantine tank fully cycled and parameter-matched before the box lands. For your first chili rasbora purchase, the LFS route is the safer bet — you can verify the fish are healthy and eating before you commit.

Quick Reference#

• Adult size: 0.8 in (2 cm)
• Lifespan: 4-8 years
• Tank size: 5 gallons minimum, 10+ gallons preferred
• Group size: 8 minimum, 12-20 ideal
• Temperature: 72-80°F (22-27°C)
• pH: 5.5-7.0 (optimal 6.0-6.5)
• Hardness: 1-5 dGH
• Filtration: Sponge filter, very low flow
• Diet: Micropredator — baby brine, daphnia, micro worms, micro pellets (under 0.5 mm)
• Feeding: 2x daily, small portions
• Best tank mates: Ember tetras, pygmy corys, sparkling gouramis, neocaridina/caridina shrimp
• Avoid: Any fish over 1.5 in, fin-nippers, goldfish, livebearers
• Difficulty: Beginner-friendly with stable, soft, slightly acidic water
• Lighting: Low to moderate; floating plants for cover
• Decor: Heavy planting, Indian almond leaves, driftwood for tannins