The direct answer for an ageing corydoras
An ageing corydoras eats best when food is delivered to the floor of the tank, close to the spot where it already rests, in a form soft enough for worn barbels to handle. This catfish was never built to chase flakes at the surface. It shuffles along the substrate, tasting its way through the sand, and an older fish does that shuffling more slowly, with less stamina for competing against quicker midwater tankmates. So the fix is placement and texture: a softened sinking pellet or wafer fragment set down on open sand near its shelter, offered at the dim end of the day when corydoras instincts say it is time to forage.
Why an older corydoras quietly misses meals
A senior corydoras can look fine while eating far less than it needs. Its barbels, the whiskers it uses to locate food, wear shorter with age and past substrate irritation, so each bite takes longer to find. Younger tankmates learn that dropped food is fair game and strip the bottom before this catfish arrives. Strong filter flow skids light food across the tank, away from the corner where the corydoras rests. None of this shows up as drama; the fish simply gets thinner behind the head while the rest of the tank looks well fed, which is why the change is so often spotted late.
Setting food down where this catfish actually rests
Pick the patch of fine sand your corydoras returns to most evenings and make that the feeding station. Drop a pre-soaked sinking pellet or a broken piece of wafer there with tongs or a feeding tube so it lands in the same square of substrate every time. Feed after the main lights dim, when this nocturnal-leaning catfish is most willing to search. If the current slides the food away, baffle the outflow or add a smooth stone as a windbreak on the upstream side of the patch. Feed the surface and midwater fish at the far end first, so their commotion buys the corydoras an undisturbed minute on the bottom.
Texture, timing, and the barbel check
Hard, dry pellets are work for an old corydoras. A few minutes in a cup of tank water softens a pellet so the fish can mouth it apart instead of worrying at a rock-hard lump. Smaller pieces beat one large wafer when several ageing corydoras share the tank, because each fish can claim a fragment rather than crowding a single disc. Once a week, watch the barbels at close range during feeding: they should look even and full-length for this fish. Shortened, frayed, or reddened barbels point to rough substrate or fouling in the sand, and stirring waste out of the feeding patch with a gentle siphon helps the feelers recover their working surface.
When a feeding change becomes a vet question
Book a vet visit if your corydoras stops coming to the feeding patch altogether, loses visible weight along the back, or breathes fast while resting on the bottom. Barbels eroded down to nubs, white patches on the body, or a fish isolating itself away from its group are also reasons to get professional eyes on it promptly rather than adjusting food again. Bring notes on when the appetite faded and what the tankmates are fed, because that timeline helps the vet separate a feeding-access problem from illness. Writing those appetite and barbel observations into KinsLe's Pet Passport before the visit means the vet reads this corydoras's recent history in one tidy packet instead of relying on your memory at the counter.