A practical guide to chilli rasbora care, covering tank size, water parameters, feeding, and setup. Learn how to keep Boraras brigittae healthy, settled, and displaying their best colour.
Tiny, vibrant, and often described as one of the best nano fish available, chilli rasboras (Boraras brigittae) have become a firm favourite among aquarists. Their glowing red colour, peaceful nature, and suitability for smaller aquariums make them an appealing choice.
However, despite their popularity, many fishkeepers do not succeed with this species. People sometimes say they are a good beginner fish thanks to their small size, but in reality, they can be surprisingly sensitive. Poor and unstable water conditions can cause their colours to fade. In extreme cases, chronic stress can leave them vulnerable to disease, leading to their gradual decline and potentially death.
In this guide, we will outline everything you need to know about chilli rasbora care including: ideal tank size, water parameters, feeding, and compatible tank mates. Perhaps most importantly, we will focus on what actually works in real home aquariums, and how to keep them bright red!
Related article: The 75 most colourful fish.
All photos by Alex Bell
Chilli Rasbora Fact File
Scientific name: Boraras brigittae
Size: up to 2cm (0.8”)
Origin: Found in the south of Borneo.
Habitat: Lives in the peat swamps with still or slow-moving waters. Aquatic plants are limited due to the lack of light penetration through the tannin-stained waters, but marginal and overhead cover is often dense.
Tank size: 45x25x25cm (18x10x10”)
Water requirements: Soft and acidic conditions are best, with a pH below 7 and a hardness below 8°H.
Temperature: 20-28°C (68-82°F)
Temperament: Their small size and peaceful nature mean they can be outcompeted in a busy tank with boisterous larger fish. Otherwise, a perfect addition to a carefully planned community tank, or indeed an aquascape or biotope.
Feeding: Their nano size means they require suitably small foods. Prepared micro granules or crushed flakes, and small frozen and live foods like Cyclops and baby brine shrimp work well.
Availability & cost: Common in stores as they are a great option for the larger end of the nano aquariums. Prices tend to start from £3 each.
What is the ideal tank for chilli rasboras?
Their tiny size means almost everything is a potential predator. To see them at their best, they need plenty of cover and a good-sized group of their own kind to feel secure. To keep a proper group, tank space becomes a key consideration – which brings us to tank size.
How small is too small for chilli rasboras?
While Boraras brigittae are an ideal nano aquarium fish, there is a lower limit to what is suitable. Two key factors determine a suitable chilli rasbora tank size. There should be enough space for a good size shoal and enough water to maintain a stable environment.
A 20 litre (4.4 gal) aquarium is more likely to experience harmful swings in water quality than a 45 litre (9.9 gal) one. Even small swings that won't immediately kill the fish will stress them, making them more susceptible to disease and reducing their colours. Similarly, a shoal of 10 or more rasboras will be a squeeze in the 20 litre (4.4 gal) tank, but more suitable for a 45 litre (9.9 gal).
We also need to think about the dimensions of the aquarium, as it is not all about volume! While these fish are small, they are fairly active and a wider tank is far more suitable than a tall one. A 50x30x30cm (20x12x12") tank will be far more suitable than a 35x35x35cm (14x14x14") one, despite holding similar volumes.
Related article: Top 10 small fish for nano aquariums.
Aquascaping a tank for Boraras brigittae
With the right sized aquarium, it is now time to think about aquarium décor. For chilli rasboras, also commonly known as mosquito rasboras, dense areas of cover are a non-negotiable. However, we as fishkeepers have some options on how to provide this cover and still get great results.
Option 1: Blackwater aquariums
Chilli rasboras come from the peat swamps of Borneo, here they live in dark stained waters filled with fallen branches and leaves. An aquarium that replicates their natural habitat will certainly help your tiny rasboras feel safe and settled.
Decorate the aquarium with a thick layer of leaf litter and some aquarium safe wood and you are almost there. Plus, this is an incredibly cost effective aquarium as you can collect the leaf litter for free! While locally collected leaves will not create a true biotope aquarium, they function in the same way as the leaves in Borneo.
You can also add some houseplants growing out the top of the tank to replicate the overhead canopy of trees. A handful of floating plants can also help provide this much needed shade. They will also help soak up wastes and the fish will love exploring in the roots looking for food.
Watch us create a simple blackwater scape for chilli rasboras here!
Option 2: Planted aquariums
Fortunately, these fish will also thrive without decaying materials and tinted water. They can work just as well in a beautiful underwater garden as the dense aquarium plants provide the cover and shade they need. Equally, aquarium soils and CO2 lower the pH creating the acidic conditions these fish thrive in.
Chilli rasboras generally prefer more dimly lit conditions. Therefore, low tech plants with a less powerful light is probably best for your nano aquascape. Java ferns, picture below, work great alongside chilli rasboras and are a perfect beginner friendly species.
Related article: 5 easy and beautiful stem plants for your aquascape.
However, they can do well in higher energy systems if provided enough shelter and the red colouration pops in a brightly lit aquarium. Indeed, an RGB plant LED light can enhance this red even further! It would be advisable to wait until the plants have grown in and are providing plenty of shade before adding the shoal of chilli rasboras.
Watch our editor's high tech aquascape which features colourful chilli rasboras here!
Do chilli rasboras need soft water?
Yes, chilli rasboras are naturally adapted to thrive in acidic and soft water. While captive breeding may have enabled these fish to survive in a pH above 7, they will not show their best colours in these conditions.
If you have soft and acidic tap water, that is perfect. However, if you live in areas with liquid rock coming out of your tap you'll need to find a solution.
Reverse osmosis (RO) water is often the best choice for achieving the soft, acidic conditions chilli rasboras require. This purified water will have negligible carbonate hardness allowing the pH to be easily manipulated.
Rainwater can also work as it is soft and acidic, but you must filter it before use. Run a small internal filter filled with polishing filter wool and activated carbon in a bucket of rainwater overnight. Also, it is only suitable in areas where there's no pollution.
Stability is key. If you cannot reliably provide the water these fish require it is best to avoid housing them rather than risk widely fluctuating water conditions.
For hardwater areas, consider the copper harlequin or lambchop rasbora (Trigonostigma espei) as a suitable alternative. They live in karst streams which have higher levels of dissolved minerals but do grow a little larger reaching 3cm (1.2").
Suitable tank mates for chilli rasboras
Choosing suitable tank mates for chilli rasboras is essential. Anything large will see them as food and anything boisterous may outcompete them. In nano tanks they are best housed alone in a species only aquarium or alongside Neocaridina shrimp, as they are fairly shrimp safe. This allows you to have a larger shoal of chilli rasboras, creating a more attractive and natural display.
In larger aquariums other species of tropical fish can work alongside them as long as they thrive in similar conditions. Small tetras like ember tetras, corydoras, pencilfish and other rasboras can work great in a mixed community.
For a more biotope inspired community, consider Sundadanio, wild Bettas, Parosphromenus, chocolate gouramis and kuhli loach.
Chilli rasbora tank setup summary
- Dense areas of cover in the form of live plants or botanicals.
- Shaded areas from floating plants or emergent houseplants.
- Gentle water flow mimicking the calm waters of the peat swamp.
- Shaded areas for the fish to retreat to, or dim lighting.
- Soft and acidic water.
- Peaceful and small tank mates.
FAQs on chilli rasbora care
Why are my chilli rasboras pale and not colouring up?
Chilli rasbora's colour develops over time and as they settle. Newly purchased fish take many months to be at their best. If you have had them for a long time, double check that you are following the care guide above. A slightly aggressive tank mate, not enough cover, or the incorrect water parameters can all contribute to faded colouration.
If everything else looks good, check the food. Old flake foods that have been open for a while lose their nutritional value and may be preventing your chilli rasboras from thriving. Dry foods must be used within six months of opening and then replaced. Invest in some good quality micro granules and flakes to offer some variation alongside some small frozen and live foods.
How do you breed chilli rasboras (Boraras brigittae)?
Chilli rasboras are continuous spawners, laying eggs daily once they are mature. These eggs are scattered amongst the plants or botanicals and the parents show no parental care. In some cases fry may emerge on their own but typically separating pairs into spawning tanks will be required.
Java moss works as a good spawning medium, which can be placed on a mesh bottom to allow eggs to fall through out of reach. The water must be soft and acidic, negligible carbonate hardness and a pH below 6.5. The water should be at their upper range, so in excess of 25°C (77°F).
Introduce a pair or small mixed group to the spawning tank after conditioning them with plenty of live foods. Leave the fish for a couple days before removing them, and eggs should begin hatching soon after. The tiny fry need tiny foods, have an infusoria culture going in preparation, introducing tiny fry powder, baby brine shrimp and micro worms as they grow.
My rasboras don't look like these photos, is it possible I have a different species?
Yes, it certainly is possible as there are six different species in the genus Boraras and they can sometimes get mixed up. Once you know what you are looking for it is easy enough to tell them apart, but in a busy shop tank individuals are easy to mix up.
Read our full guide to the Boraras genus to see images of some of the other common species in the hobby. You may find your 'chilli rasboras' are actually an exclamation point, or least, rasbora (Boraras urophthalmoides).