Corydoras are among the most social fish in the hobby, and they should be bought as a school, not as a pair of cleaners. Six of the same species is the working minimum, and eight to twelve is where their behaviour opens up: the group rests in a loose row, wakes together, and works across the sand in a shuffling line with barbels twitching. A lone cory or a pair will survive, but they will spend much of the day motionless under cover, and that stillness is the fish telling you the arrangement is wrong.
Why the species on the label matters
Shops often sell several cory species side by side, and it is tempting to take two of each. The fish do not see it that way. Corydoras shoal most tightly with their own kind, recognising pattern and size, so three species in pairs can behave like three separate, undersized groups sharing a tank uneasily. Pick the species whose adult size suits your aquarium, whether that is a compact pygmy type for a small tank or a larger bronze or sterbai for a bigger one, and buy the full school from that single row. Mixed groups are not a welfare disaster, but one true school is visibly calmer.
Sand, food and the bottom of the tank
A school only thrives if the floor of the tank is built for it. Fine sand lets corydoras sift and dig without eroding the delicate barbels they use to taste for food, while sharp gravel is a common cause of the worn barbels and infections blamed on the fish themselves. They are not a clean-up crew that lives on leftovers, so feed them deliberately with sinking foods that reach the bottom after the mid-water fish have eaten, ideally as the lights dim. A group fed properly will show round bellies and constant gentle activity rather than frantic scavenging.
Watching a school for early trouble
Because they move as a unit, corydoras make health changes easy to spot once you know the group's normal. One fish sitting apart, breathing fast while the others rest calmly, or failing to join the evening forage stands out against the pattern. Watch also for the whole group making repeated dashes to the surface, which can be normal air-breathing in moderation but signals low oxygen or irritated gills when it becomes constant. Note which fish, when it started and what changed in the tank, and seek advice from an aquatic vet or experienced shop promptly if an individual fades while the school stays well.
Sharing the care of a bottom crew
A school of corydoras creates quiet recurring work: sinking food delivered after the tetras have eaten, sand sifted during water changes, a headcount that actually counts fish who hide in the same plant. Those jobs are easily dropped when they live in one person's head, and the fish at the bottom are usually the first to be underfed by accident. Dividing those checks through KinsLe's Care Teams lets family members take turns feeding the school and checking the substrate, with each completed task marked and timestamped so the corydoras are cared for on schedule rather than on memory.