A chili rasbora is one of the smallest fish in the aquarium hobby - adults stay under an inch - so the internet minimum of 5 gallons sounds generous. Five gallons can work in experienced hands, but a 10-gallon tank is the honest recommendation for most people. The extra water is not about swimming room; it is about stability, because a pinch too much food or a hot afternoon swings temperature and chemistry far faster in five gallons than in ten. A 10-gallon also fits the school of ten or more that this shy fish needs before it will come out and be seen.
Ten fish minimum, and more is better
Chili rasboras live or die socially by group size. Kept in fours and fives they hug the plants, eat nervously, and stay a washed-out orange. In a school of ten or more the same fish spread across the tank, feed in the open, and the males deepen to the ruby red that gives the species its name. A larger school also spreads the males' sparring so widely that no single fish becomes a target. If the tank can hold fifteen without crowding the other residents, take fifteen - the behavior difference between ten and fifteen is still visible. Buy the group all at once if you can, so no small first batch spends weeks hiding while it waits for reinforcements.
Water like a peat swamp
In the wild, chili rasboras live in slow, tea-colored streams and peat swamps in Borneo, where the water is soft, acidic, and stained with tannins. Recreate the feel rather than chasing exact numbers: driftwood and dried leaves to tint the water, gentle filtration, and temperatures in the upper 70s to low 80s Fahrenheit. Stability matters more than hitting a textbook figure - a tank that holds the same soft, warm conditions week after week suits this species better than constant adjusting. Dim or plant-shaded light completes the picture; under a bare bright light these fish read the tank as exposed and stay low among the leaves.
Feeding a mouth that small
An adult chili rasbora's mouth is tiny, and standard flake pieces are simply too big to bother with. Crush food fine, offer small live or frozen foods such as baby brine shrimp and microworms where you can, and feed little amounts daily rather than a feast every few days. They are slow, polite feeders, so in a mixed nano tank, watch that faster fish are not finishing everything first. Uneaten food is the main threat in a tank this size: what a chili school misses in the morning is fouling the water by evening, which is why small water changes on a schedule beat occasional big ones.
Keeping tiny jobs from being done twice
A nano tank runs on small, frequent jobs - a pinch of food, a jug of changed water, a quick count of the school - and in a shared household those jobs are easily doubled or skipped entirely. Put names on them instead. KinsLe's Care Teams lets you assign this tank's feeding and water changes to specific people, and each finished task is marked with a timestamp, so the evening feeder can see the morning feeding already happened.