If the aquarium hobby kept an official peace ranking, corydoras would sit at the top of it. A cory has no territory, no rivalries, and no interest in other fish at all: it will not nip fins, chase a smaller tankmate, guard a corner, or compete for a mate in any way that troubles a community. Groups spend the day nose-down in the substrate, bumping shoulders with their own kind and flowing around everyone else like water around stones. For a beginner building a first community, they are the safest possible addition.
Peaceful in both directions
Their peacefulness runs both ways, which is rarer than it sounds. Corys are not only harmless to others; they are almost impossible to provoke and too sturdily built to be bullied by the mild showing-off of gouramis or rams. They share space comfortably with tetras, rasboras, livebearers, dwarf gouramis, otos, snails, and adult shrimp, and even most bettas ignore them completely. One honest footnote: peaceful is not the same as harmless to eggs and newborn fry. A cory that finds fish eggs or a just-hatched fry on its rounds will eat it, the way it eats anything edible on the bottom.
The one real problem: dinner
Every conflict involving corys in a community tank is about food, and the cory is always the loser. Quick mid-water fish — danios, many barbs, enthusiastic livebearers — strip the water column bare in the first minute, and the pinch of flakes that reaches the bottom is nowhere near a meal for a bottom-feeding school. Tanks full of fat tetras and quietly starving corys are a genuine beginner pattern. The fix is deliberate feeding: a sinking wafer or pellet per small group, dropped in after the main feed or near lights-out when the corys forage most actively, placed where you can watch it actually get eaten.
Their social life is their own school
Corys reserve all their social energy for each other. Five or six of the same species will rest in a row, feed in a scrum, and shoot to the surface in formation; two or three stay timid and nocturnal. Mixing species is peaceful but not social — a bronze and a panda will pass without a flicker — so build one proper school of a single species rather than a sampler of singles. Their contentment is contagious in the other direction, too: relaxed bottom dwellers cruising openly tell shy mid-water fish the tank is safe, and the whole community shows itself more.
Arranging the tank so peace holds
Give the school what it needs to stay itself: smooth sand to sift, a cave or plant thicket to retreat under at midday, and open bottom where the group can feed together. Keep the water clean and the routine boring — corys ask for so little socially that their care is almost entirely water and food. Watch at feeding time that each fish eats with the group; the one hanging back from a species that lives for the scrum is the one worth a closer look and a water test.
In a shared household, the dinner problem usually comes down to who fed what — one person scatters flakes, another forgets the wafers entirely. With Family Sharing in KinsLe, the cory school's profile can be passed to household members you pick, and each person named can open that profile for themselves.