Harlequin rasboras are schooling fish in the strict sense, and their minimum number is six, with eight to ten or more being where the species truly performs. In a proper school they hold a loose, shimmering formation in the middle of the tank, tilting and turning together, the black wedge on each flank flashing as they change direction. In twos and threes they do none of this. They scatter into the planting, hold still for long stretches and look like a different, duller fish, which is why so many keepers underrate a species that simply needed more of its own kind around it.
What a bigger school changes
Security is the mechanism behind the display. A rasbora in a large group can afford to feed in open water because dozens of eyes are watching for danger and dozens of bodies dilute any threat, real or imagined. Males colour up to a deeper copper and court females with trembling displays near broad leaves, where harlequins glue their eggs underneath in a spawning ritual worth the tank space by itself. None of that behaviour needs special equipment; it needs numbers, a dim or planted backdrop and water that stays steady, because a school treated to constant change spends its confidence as fast as it builds it.
Building the tank around the school
Harlequins come from soft, shaded forest water, and a tank with a planted rear and sides, subdued light and an open central lane suits them best. They mix well with other peaceful fish of similar size and temperament and are poor companions for boisterous or fin-nipping species that break the school's calm. Feed small foods that fit small mouths, spread across the surface so the whole formation eats, and keep the group in mind when choosing tank mates: a school of ten harlequins plus a few calm bottom dwellers is a more coherent aquarium than the same ten fish scattered among restless larger species.
Buying and settling the whole group
Choose the school in one purchase from a tank of bright, level-swimming fish, favouring individuals with the wedge marking sharp and the belly full, and add them together so the school forms immediately rather than in anxious instalments. Quarantine matters most when they are joining other fish, since a school bought from one source shares one history. In the first week, expect the group to hold tighter and feed more cautiously than it will later; a fish still isolated and colourless after the school has settled is the one to examine, because harlequins that feel well travel with the group almost without exception.
The small jobs a school creates
A school makes some care tasks easier, since appetite and mood can be read at a glance, and a few quietly specific: spreading food so the last fish in the formation eats, counting heads that all look alike during a water change, and noting when the school's behaviour shifts after a new plant or tank mate arrives. Those checks are simple but easy to skip when visitors feed the tank or the usual keeper is away for a weekend. Sharing them through KinsLe's Care Teams means the people looking after your harlequins each know their tasks, and every completed feeding or check is marked off for the next person to see.