---
type: species
title: "Phoenix Rasbora Care Guide: The Nano Schooling Fish from Borneo"
slug: "phoenix-rasbora"
category: "freshwater"
scientificName: "Boraras merah"
subcategory: "Rasbora"
lastUpdated: "2026-04-24"
readingTime: 9
url: https://www.fishstores.org/species/phoenix-rasbora
---

# Phoenix Rasbora Care Guide: The Nano Schooling Fish from Borneo

*Boraras merah*

Master Phoenix Rasbora care. Learn about Boraras merah water parameters, diet, breeding, and why they are the perfect nano fish for planted tanks.

## Species Overview

Phoenix rasboras (*Boraras merah*) are micro-schooling cyprinids from the peat swamps of southern Borneo, prized in nano aquascaping for their flame-colored bodies and confident shoaling behavior. They top out under three-quarters of an inch, which lets a serious school fit into a tank smaller than a kitchen drawer — and few freshwater fish put on a better display per gallon when their environment is dialed in.

They sit in the same genus as the more famous chili rasbora and share most of its care requirements: soft, acidic, tannin-stained water and tiny, frequent meals. Get the chemistry close to their wild Borneo home and a group of 12 will color up like glowing embers drifting through your planted tank.

| Field       | Value                            |
| ----------- | -------------------------------- |
| Adult size  | 0.7 in (1.7 cm)                  |
| Lifespan    | 3-5 years                        |
| Min tank    | 5 gallons (school of 6+)         |
| Temperament | Peaceful, shoaling               |
| Difficulty  | Beginner with soft, acidic water |
| Diet        | Micropredator                    |

> **The genus Boraras: chili-rasbora cousins**
>
> *Boraras merah* belongs to a genus of seven described "micro-rasboras" that includes the chili rasbora (*B. brigittae*), dwarf rasbora (*B. maculatus*), least rasbora (*B. urophthalmoides*), and exclamation-point rasbora (*B. naevus*). Every species in the genus shares two defining traits: a mouth gape under half a millimeter and a strict preference for soft, acidic blackwater. If you can keep one *Boraras* species, you can keep them all — and many aquarists collect the genus as a hobby.

### Distinguishing *Boraras merah* from *Boraras brigittae* (Chili Rasbora)

The two species look superficially identical at first glance — both are tiny, red, and stripe-bearing — but the lateral marking is diagnostic. *Boraras merah* shows a broken black midline that often resolves into a thick blotch or spot near the tail, while *Boraras brigittae* carries a clean, continuous stripe from gill to caudal peduncle. Phoenix rasboras tend to wear a more orange-red color compared to the deeper crimson of mature chilis, and the body marking pattern reads as "blotchy" rather than "striped."

Stores frequently mislabel the two, partly because importers sometimes lump them under the same trade name and partly because juveniles of both species look alike. If you specifically want phoenix rasboras, ask the staff to identify the lateral marking and check for that broken-stripe pattern in the bag.

### Natural Habitat: The Blackwater Streams of Borneo

Phoenix rasboras come from the peat-stained streams and forested swamps of southern Borneo, particularly in the Indonesian provinces of Central and South Kalimantan. The water in these habitats runs the color of strong tea — heavy with tannins from decomposing leaf litter and submerged wood — with pH frequently below 5.0 and total hardness measuring near zero. The substrate is dark organic mulch, the canopy is dense, and the visible light at fish level is dim and dappled.

That extreme chemistry shapes everything about how the fish look and behave. In bright open water with hard, alkaline tap water, they go pale and skittish. In a tannin-tinted nano tank with floating cover, they color up within hours and start exploring the open water column.

### Maximum Size and Lifespan Expectations

Adults rarely exceed 0.7 inches (1.7 cm) — even smaller than the chili rasbora. This is one of the smallest freshwater aquarium fish in the trade, full stop. Females are slightly larger and rounder when carrying eggs; males are slimmer with more saturated coloration.

Lifespan in a stable tank runs 3 to 5 years. They are not as long-lived as some larger schooling fish, but their tiny body size puts a natural ceiling on longevity. Most premature deaths come from fish-in cycling, sudden parameter swings during water changes, or undetected pathogens introduced with new tank mates.

## Water Parameters & Tank Requirements

Phoenix rasboras are not technically demanding, but their tiny body mass means there is no room for parameter swings. A drop of ammonia that an adult tetra would shrug off can wipe out a school overnight. Get the chemistry locked in before the fish arrive, and stability becomes the main maintenance goal.

### Ideal Nano Tank Size (Minimum 5-10 Gallons)

A 5-gallon planted tank is the realistic minimum for a starter school of 6-8 phoenix rasboras. They are tiny and they don't move much, but anything smaller leaves no buffer for evaporation, temperature swings, or feeding errors. A 10-gallon planted tank is the practical sweet spot — it comfortably houses 12-15 phoenix rasboras alongside a colony of cherry shrimp and a dwarf bottom-dweller.

Curved-front nano tanks like the [Fluval Flex](/guides/fluval-flex) (9 or 15 gallon) are nearly purpose-built for this species: built-in filtration with low return flow, room for floating plants and dense midground planting, and an enclosed-cube look that recreates the shaded canopy of their natural habitat.

> **Schooling 6+ for full color display**
>
> Phoenix rasboras are obligate shoalers. A group of 3 or 4 will spend most of its time hiding behind the filter intake and never display its full coloration. A school of 6 is the minimum for natural behavior, but the visual payoff jumps significantly at 12+ fish — you'll see active group movement, dominance displays from males, and the deep red color the species is known for. Plan your stocking around schooling needs, not your gallon limit.

### Soft, Acidic Water: Targeting pH 4.5-6.5 and Low GH

Wild populations live below pH 5.5 in near-zero-hardness water. Tank-bred specimens — which now make up the majority of imported stock — handle a wider range, but stay well under pH 7.0 for long-term health. Aim for pH 5.5-6.5 in the home aquarium, with the lower end favored if you plan to breed.

Hardness should sit between 1 and 4 dGH. If your tap water reads above 7.5 pH or above 7 dGH, blend it with RO water at roughly 50/50 to soften and acidify before water changes. Botanicals — Indian almond leaves, alder cones, and oak leaves — gradually lower pH and release the tannins these fish evolved with. One Indian almond leaf per 5 gallons, replaced every 2-3 weeks, is a low-effort baseline.

> **Blackwater enhances vivid red coloration**
>
> Tannin-stained blackwater isn't just an aesthetic choice — it's a direct color trigger for phoenix rasboras. The deep red pigmentation is camouflage against a dark, dim swamp floor, and the fish flush their fullest color only when the surrounding environment matches that visual context. A tank with one or two Indian almond leaves and a piece of Malaysian driftwood will produce noticeably redder fish than the exact same tank with crystal-clear water. Add cover overhead with floating plants like red root floaters or salvinia for the strongest effect.

### Temperature Stability (74°F-82°F)

Target 76-80°F as the daily setpoint. They tolerate the broader 74-82°F range, but stability matters more than the exact value. In a 5-gallon nano tank, a malfunctioning heater can swing the temperature 6-8 degrees in a few hours, which is enough to kill a sensitive school. Use a reliable adjustable heater with an external thermostat or a thermostat-controlled outlet — not a cheap preset stick-on heater.

Run a thermometer at the opposite end of the tank from the heater and check it daily for the first week. Once you confirm a stable hold, weekly checks are enough.

### Low-Flow Filtration and the Importance of Floating Plants

A sponge filter is the standard recommendation for phoenix rasbora tanks. It provides gentle biological filtration without the ripping current of a hang-on-back filter, and the porous sponge surface is shrimp-fry-safe. For a 10-gallon nano with phoenix rasboras and shrimp, a single sponge filter rated for 20 gallons is appropriate.

If you prefer a hang-on-back or small canister, baffle the output with a sponge prefilter or a flow diffuser. Phoenix 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, dial it back.

Floating plants — red root floaters, dwarf water lettuce, salvinia, frogbit — diffuse light, provide cover, and recreate the canopy these fish evolved under. They also soak up excess nitrate and shade out algae. A handful of floaters in any phoenix rasbora tank is the single highest-payoff piece of decor you can add.

## Diet & Feeding

Phoenix 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.

### Micro-foods: Baby Brine Shrimp, Moina, and Cyclops

The best staple foods are small live and frozen items: freshly hatched baby brine shrimp, daphnia, moina, micro worms, vinegar eels, and cyclops. These match natural prey size and trigger active hunting behavior across the tank. Live foods produce noticeably better color and breeding behavior than dry alternatives.

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

### Selecting High-Quality Crushed Flakes and Pellets

Dry food works for phoenix 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 for High-Metabolism Nano Fish

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. A pinch of crushed flake or a teaspoon of just-hatched baby brine for a school of 12 is plenty.

Skip a feeding day every 7-10 days to give their systems a break and let the bioload settle. Phoenix rasboras carry essentially no body fat reserves, but a single skipped day is well within their tolerance and noticeably reduces water quality strain in nano setups.

## Tank Mates & Compatibility

Phoenix rasboras need calm, similarly sized tank mates and zero aggression. Their adult size — barely two-thirds of an inch — puts a hard ceiling on what they can safely live with. Even peaceful 3-inch fish stress them just by existing in the same water column.

### Best Nano Tank Mates (Shrimp, Snails, and Micro-Rasboras)

The proven pairings are other peaceful nano species: [chili rasboras](/species/chili-rasbora), [ember tetras](/species/ember-tetra), [galaxy rasboras](/species/galaxy-rasbora) (celestial pearl danios), pygmy corydoras (*Corydoras pygmaeus* or *C. hastatus*), sparkling gouramis, and other *Boraras* species. Otocinclus catfish work as algae-eating tank mates, but they need a mature tank with established biofilm.

A textbook nano biotope is a 10-15 gallon planted aquarium with phoenix rasboras, 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.

### Why Large or Aggressive Fish Must Be Avoided

Avoid anything large enough to fit a phoenix 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 phoenix rasboras at feeding time), and any catfish over 3 inches. Avoid all known fin-nippers (tiger barbs, serpae tetras) regardless of size. Goldfish and phoenix 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](/guides/freshwater-fish) or ask LFS staff. The safe list for nano-fish-only tanks is short, but it's reliable.

### The Importance of Schooling (Minimum Group of 8-12)

Phoenix rasboras are obligate shoalers. A group of 4-6 in a typical store bag often sees one or two losses during transport and acclimation. Plan to buy at least 8, and think of 12-15 as the right starter group for a 10-gallon tank. A larger initial group spreads social behavior, makes individual losses less devastating to the school dynamic, and gives the dominant males something to display against.

In groups under 6, you'll see chronic stress behavior: hiding behind the filter intake, refusing to eat in the open, faded coloration, and rapid breathing. Bumping the school up to 10+ usually reverses all of those symptoms within a week.

## Breeding Phoenix Rasboras

Breeding phoenix 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.

### Conditioning Breeders with Live Foods

Sex the adults first. 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.

Condition the breeders for 1-2 weeks on a varied diet of live baby brine shrimp, daphnia, moina, and micro worms. Twice-daily feedings of live food drive the females into spawning condition faster than any prepared food. Skip the dry food entirely during the conditioning period.

### Setting Up a Spawning Mop or Moss-Heavy Breeding Tank

Move conditioned pairs (or a small group of 2 males to 4 females) to a separate breeding tank with mature, soft, acidic water (pH 5.5-6.0, sub-2 dGH hardness), java moss or a spawning mop, and dim lighting. A 2.5- to 5-gallon breeding tank is plenty.

Phoenix 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 a slight temperature bump to 78-80°F and a generous live food regimen. Remove the adults within 24 hours of seeing eggs in the moss.

### Raising Fry: Infusoria and Vinegar Eels

Eggs hatch in 24-48 hours, and fry are tiny — too small for newly hatched baby brine shrimp 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). Vinegar eels are the easiest "live first food" to culture in volume.

Switch to baby brine shrimp once the fry are large enough to handle it — usually around day 7-10. Expect a slow grow-out: fry take 3-4 months to reach saleable size. Water changes during fry rearing should be small (10% twice weekly) and parameter-matched to within a tenth of a pH unit.

## Common Health Issues

Phoenix 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.

### Sensitivity to Sudden Parameter Shifts (Osmotic Shock)

The single most common cause of death in newly acquired phoenix rasboras is osmotic shock during acclimation. They evolved in soft, acidic water with near-zero mineral content. Dropping a fish acclimated to that chemistry directly into hard, alkaline tap water (pH 7.8, 12 dGH) is a death sentence — even if both water samples test "safe" individually.

Drip acclimate over 60-90 minutes minimum, ideally longer for fish coming from a soft-water source into a moderately harder tank. Read [how to acclimate fish](/guides/how-to-acclimate-fish) for the step-by-step method. If you cannot match source water chemistry within roughly 0.5 pH units and a few dGH, prepare a holding tank that does match the source and slowly transition the fish over 1-2 weeks before moving them into the display.

### Bacterial Infections in Poor Water Quality

Bacterial infections in phoenix 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 before reaching for medication. A water change with parameter-matched water often resolves early-stage symptoms without antibiotics.

If antibiotics are necessary, dose for actual tank volume and not the labeled "average" tank size, and remove activated carbon from any filter before treating.

> **Often sold as 'fire' or 'phoenix' — naming variations**
>
> Phoenix rasboras are sold under several trade names including "fire rasbora," "merah rasbora," "Borneo fire rasbora," and occasionally just "phoenix." Some importers and retailers also lump them in with chili rasboras (*B. brigittae*) under generic "micro rasbora" tank labels, which makes shopping by common name unreliable. Always verify the species by lateral marking — phoenix rasboras show a broken stripe with a blotchy spot near the tail, while chili rasboras carry a clean continuous stripe. If the staff can't tell you the scientific name with confidence, ask to see the import paperwork or look up the supplier's listing online before you buy.

## Where to Buy & What to Look For

Phoenix rasboras are less common in the trade than chili rasboras, but most local fish stores with a serious nano-fish section will carry them or be able to order them through their wholesaler. Where you buy matters less than how the fish were handled in the supply chain.

### Identifying Vibrant Coloration vs. Stress Pale

A healthy phoenix 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 on at least the dominant fish should be a clear orange-red; 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. Watch the school for at least five minutes during your visit. Active swimming, clear eyes, and intact fins are all visible from outside the glass.

> **Buy Local**
>
> Always inspect phoenix rasboras in person before buying. Look for active shoaling, vivid orange-red coloration on dominant fish, and clean intact fins. Avoid stores where the species' tank shows obvious disease (white spots, flashing, hanging at the surface) or where the fish are still pale and bunched in a corner from recent shipping. A good LFS will let you watch the school feed before you commit.

### Questions to Ask Your Local Fish Store (LFS)

Phoenix rasboras imported fresh from Indonesia are fragile for the first 2-3 weeks in a store tank. Ask the staff how long the current batch has been in-store. The right answer is "at least a week, ideally two." A school that arrived yesterday may look fine on the shelf but is statistically much more likely to die during acclimation than one that has settled and started eating in the store.

Ask whether the store keeps them in soft, acidic water or in standard tap. If the store uses RO-blended water and tannins for the holding tanks, the fish are far better adapted to home setups that match. Ask the staff to feed the school while you watch — fish that ignore food in the store will rarely start eating in your tank without intervention.

## Quick Reference

- **Adult size:** 0.7 in (1.7 cm)
- **Lifespan:** 3-5 years
- **Tank size:** 5 gallons minimum, 10+ gallons preferred
- **Group size:** 8 minimum, 12-15 ideal
- **Temperature:** 74-82°F (23-28°C), target 76-80°F
- **pH:** 4.5-6.5 (target 5.5-6.5)
- **Hardness:** 1-4 dGH
- **Filtration:** Sponge filter, very low flow
- **Diet:** Micropredator — baby brine, daphnia, moina, cyclops, micro pellets (under 0.5 mm)
- **Feeding:** 2x daily, small portions
- **Best tank mates:** Chili rasboras, ember tetras, galaxy rasboras, pygmy corys, neocaridina shrimp, snails
- **Avoid:** Any fish over 1.5 in, fin-nippers, goldfish, large livebearers
- **Difficulty:** Beginner-friendly with stable, soft, acidic water
- **Lighting:** Low to moderate; floating plants for cover
- **Decor:** Heavy planting, Indian almond leaves, driftwood for tannins

## Frequently Asked Questions

### How many Phoenix Rasboras should be kept together?

You should keep a minimum of 8 to 10 Phoenix Rasboras, though 15+ is ideal. As a shoaling species, they rely on group numbers to feel secure. In smaller groups, they become shy, lose their vibrant red coloration, and may hide constantly, leading to increased stress and a weakened immune system.

### Are Phoenix Rasboras the same as Chili Rasboras?

No, though they are closely related. Boraras merah (Phoenix) features a broken black mid-line with a distinct spot, whereas Boraras brigittae (Chili) has a solid, continuous dark stripe. Phoenix Rasboras are generally slightly smaller and have a more "blotchy" red pattern compared to the solid red of the Chili.

### Can Phoenix Rasboras live with Cherry Shrimp?

Yes, Phoenix Rasboras are one of the safest fish for shrimp colonies. Due to their tiny mouths, they are physically unable to eat adult shrimp and rarely bother juveniles. While they might snack on a brand-new shrimplet, dense moss provides more than enough cover for the colony to thrive.

### Do Phoenix Rasboras need a heater?

Yes, they are tropical fish from Borneo and require stable temperatures between 74°F and 82°F. Because they are often kept in nano tanks (under 10 gallons), using a reliable, adjustable heater is critical, as small water volumes are prone to rapid temperature fluctuations.

### Why is my Phoenix Rasbora pale?

Paleness is usually caused by stress, poor water quality, or lack of cover. Ensure your pH is not too high (keep it below 7.0) and provide plenty of plants and tannins. If the fish were recently moved, they may take several days to regain their deep orange-red hue.

---
*Source: [FishStores.org](https://www.fishstores.org/species/phoenix-rasbora)*
*Last updated: April 24, 2026*