Corydoras meals are measured at the bottom of the tank, where the fish actually live. A working portion for a typical group is roughly one small sinking pellet or a broken wafer section for every two or three cories, dropped onto open substrate near where the group rests. The cories will converge, shuffle through it with their barbels, and work it down over the next twenty minutes or so. Food still sitting untouched after half an hour means the portion was larger than the group needed.
Leftovers are not a feeding plan
The persistent myth is that corydoras thrive on whatever the other fish miss. They do not — falling scraps are a supplement at best, and a cory fed only on leftovers slowly thins while the surface fish thrive. Corydoras are proper feeders with real appetites, and in the wild they spend hours sifting sediment for worms and insect larvae. Their tank meal should be deliberate food in deliberate amounts: sinking pellets, small wafers, and rotating frozen bloodworms or daphnia that you place where the shoal can reach them first.
Getting the food past the mid-water fish
The amount question is really a delivery question in a community tank. Flake scattered on the surface may never reach the bottom in quantity, so the sinking portion has to go in as its own event: drop it in one spot, ideally just after the main fish have had their surface feed and lost interest, or as the lights dim and the cories become bold. Watching a full feed once teaches you more than any chart — you can see whether each cory in the group gets its head down, or whether the boldest two monopolize the pellet while the shy ones hover.
Portions change with the group
A trio of cories and a shoal of twelve do not scale in a straight line, because more fish graze more of the tank between meals. Scale by observation instead: the group's bellies should look gently rounded from the side, barbels intact and busy, and the substrate clean of decaying pellets by the next morning. Young, growing cories and females in breeding condition earn the generous end of the range. If you breed them, fry in the tank need their own tiny foods at the bottom rather than a bigger adult portion scattered wider.
The signs the amount is wrong
Too little shows as restless, constant foraging with thin bodies and fraying condition across the whole group. Too much shows as pellets blackening on the substrate, a film of waste in the corners the cories sift, and water that clouds despite the filter keeping up. Barbel erosion is a warning worth acting on — it is linked to dirty substrate far more than to the gravel itself, and it starts with uneaten food rotting where they feed. Keep portions honest, siphon the feeding corner during water changes, and ask an aquatic vet about persistent barbel loss or a group that stops feeding together.
Because cory food goes in at different times and in different forms from the surface feed, a shared note of the sinking portion in KinsLe's Care Teams — assigned, timed, and marked done — stops the shoal being fed twice or forgotten entirely.