A school that stresses as one
Harlequin rasboras are peaceful mid-water schoolers, and their security comes from the group: a settled school hovers together in open water, copper colours bright, while a frightened one either scatters into the plants or freezes in a tight knot near the bottom. Anything sudden — a lid banged open, a hand diving in, a siphon arriving without warning — triggers that response, and repeated frightening cleans teach the school to hide whenever anyone approaches the tank. The fish themselves are not fragile; they simply need cleaning to be boring. Predictability, more than any product or technique, is what keeps harlequins calm.
Make your arrival uninteresting
Open the lid slowly and let the school watch your hands move unhurriedly above the water for a moment before anything goes in; rasboras settle quickly once movement proves slow. Soften bright room lighting if you can, and have the temperature-matched, dechlorinated refill water ready so the session flows without long pauses that leave the tank half-drained. Start your work at the end of the tank furthest from where the school is hovering, so the fish always have the far, undisturbed end — ideally the planted end — as their refuge throughout.
Slow passes, shelter left standing
Siphon in short, steady passes just above the substrate, lifting settled waste without excavating planting soil or churning debris into the water column the school swims in. Clean the glass in long, slow strokes. Crucially, do not thin, move or remove the plants and shaded corners the harlequins retreat to, and never take out every decoration in one visit — a school whose shelter vanishes mid-clean has nowhere to process the disturbance. Rinse filter media in removed tank water, keep each change moderate, and refill by pouring against the glass so the current does not scatter the group. If you must net a fish for any reason, that is a separate, planned job — not something to improvise during a clean, because one chased harlequin panics all of them.
Harlequins also colour up or wash out with the water itself, which makes them honest reporters of your cleaning habits. A school kept in small, frequent changes holds that deep copper wedge vividly, while one subjected to rare, large swings tends to stay pale for days afterwards. If your fish fade after every clean, treat the colour itself as the measurement: halve the change, double the slowness of the refill, and watch whether the school keeps its colour through the next session.
The look of a school that coped
Within half an hour of a calm clean, the school regroups in open water, colours back up, and the fish resume their loose, drifting formation. A group still pressed into the plants at feeding time, or individuals hanging apart from the school, suggests the session was too sudden or too large; shorten the next one and slow the refill further. Tracking each session and how quickly the school regrouped in KinsLe through Care Teams helps everyone who maintains the rasbora tank reproduce the same quiet approach.