Corydoras bring peace — and one condition of their own
A corydoras is close to the perfect community citizen: armoured, entirely peaceful, active at hours when other fish rest, and so uninterested in conflict that it will share a cave rather than argue over one. But corys have a condition, and it is about each other. They are schooling fish in the truest sense — a group of six or more of the same species moves, rests, and forages as a loose unit, while a lone cory or a pair becomes shy, inactive, and short-lived by cory standards. So the first tank mate decision for corydoras is always more corydoras; only once the school is right does the rest of the stocking matter.
Mid-water companions that leave the bottom alone
Above a cory school, the whole gentle community catalogue opens up. Tetras and rasboras school in the middle and never descend to compete; cherry barbs weave the lower middle without touching the corys' grazing; guppies and other small livebearers live at the surface; honey gouramis drift peacefully, and even a betta — in a tank with room — usually treats corys as furniture, since they never rise to challenge him at the surface. Harlequin rasboras deserve a special mention as perhaps the most classic pairing of all. The shared rule is simple: choose fish whose lives happen in the upper two-thirds of the water, and the corys' floor stays an uncontested workplace.
Fellow bottom dwellers: who shares the floor well
The floor itself can be shared, with judgment. Kuhli loaches are ideal neighbours — they occupy the same level at different hours, sliding out at dusk as the corys settle. Otocinclus live on leaves and glass rather than the open floor. A bristlenose pleco overlaps more, but partitions the bottom by habit: pleco on wood and glass, corys on open sand, with a cave each resolving the rest. Small peaceful shrimp colonies coexist well, though corys will happily eat shrimplets they stumble on. Where sharing fails is with territorial bottom fish — cichlids guarding a patch of floor, red-tailed sharks patrolling a territory — because the cory's response to being charged is to freeze or flee, not to move house.
Fish that turn corydoras into prey or prisoners
Corydoras have one genuine defence — sharp pectoral spines and armour — and it exists because in the wild things eat them. In aquariums the risk list is predictable: large cichlids, big gouramis, and any fish whose mouth a cory fits will eventually try, and a cory lodged by its spines can harm both fish. The quieter failure is intimidation: boisterous loaches, pushy barbs, and hyperactive tank mates that monopolise the floor drive corys into permanent hiding behind the filter. A cory school you never see is a compatibility verdict, delivered daily. Choose calm, and the school will reward you by working the front glass in the open.
Feeding arrangements so food actually reaches the floor
Most cory problems in mixed tanks are starvation in slow motion. Flake eaten at the surface never reaches them; a healthy cory school needs food delivered to the floor — sinking wafers, pellets, and frozen foods dropped after the main feed, ideally in two spots so the school spreads out. They are not algae eaters and cannot live on other fish's leftovers; a round belly at lights-out is the daily check. In a family tank, that sinking share is the detail most often forgotten by whoever is feeding. KinsLe's Family Sharing puts the cory school's needs — sinking food, every day, after the surface feed — on the profile the whole family sees, so their dinner reaches them whoever holds the food tin.