Why your corydoras hug the cover
Corydoras are shoaling bottom-dwellers, and in the wild a lone cory crossing open ground is the easiest meal a heron or a larger fish will get all day. That instinct does not switch off in a home tank. A group that is too small — two or three fish — reads the whole aquarium as exposed territory, so the fish wedge themselves behind wood and plants and only dart out when the room is dark and still. Numbers change the maths: in a group of six or more, some fish are always watching while others feed, and the whole shoal relaxes. If your corys vanish whenever you approach, read it as a security report, not a personality flaw.
Give the open areas a floor they can work
Corydoras feed by sifting — pushing their snouts into the substrate and filtering out edible scraps, sensing as they go with the whisker-like barbels around the mouth. Sharp gravel wears those barbels down and makes open-ground foraging genuinely uncomfortable, so a stretch of smooth, fine sand is often the single change that brings a shy shoal out. Keep the sand area clear rather than carpeted in plants, but ring it with cover: a cave, a piece of driftwood, a clump of broad-leafed plants within a quick dash. Open ground with an escape route beside it gets used; a bare desert in the middle of the tank does not.
Feed the same open patch, at the same times
Shy corys learn a feeding map fast. Drop sinking pellets or wafers onto the same open patch of sand, twice a day at consistent times, and let the food sit — corydoras graze slowly and will not rush a meal the way mid-water fish do. For the first week, add a small extra portion just after lights-out, when the shoal already feels brave; within days they start arriving at the patch in daylight, because the night visits taught them it is safe and stocked. Keep other fish from monopolising the patch: if boisterous tankmates hoover the surface food and shoulder the corys aside, feed the mid-water fish at the far end first, then tend the cory patch.
Light, movement and patience
Bright light switched on suddenly, a tank in a walkway with people looming past, and hands going in for frequent rearrangements all push a bottom shoal back into hiding. A timer that regularises the light, a background on the back glass, and a few weeks of boring consistency do more than any product. Sit still near the tank for a few minutes each day without feeding or tapping; corys habituate to a familiar, motionless person remarkably quickly, and a fish that forages while you watch is well on its way.
When hiding is a warning instead
A whole shoal that stops coming out after being bold, fish sitting listless rather than resting alert, worn or missing barbels, and scratching against decor are different from shyness — test the water, check the temperature suits the species, and look for bullying at feeding time. A single fish hiding while the rest forage deserves a close look for injury. If the water reads clean and the behaviour does not lift within a few days, an aquatic vet or an experienced fish shop can help you work through what the tank is telling you. Keeping the routine steady while you investigate is easier when the work is shared: on KinsLe, Care Teams lets you assign the morning and evening cory feedings to different family members and see each one marked complete with a timestamp, so the shoal's confidence-building schedule holds even on busy days.