Foraging in company is the corydoras workout
A senior corydoras catfish exercises the way his kind always has, nose down in the company of his school. A foraging bout is a group event: several fish shuffle shoulder to shoulder across a patch of substrate, barbels sweeping, tails stirring up tiny clouds as they dig out buried morsels. In a senior the bouts run shorter, the patch is smaller, and the rests between them, tucked under a leaf or against a stone, grow longer. None of that needs fixing. What a senior cory needs is the school kept together, because a lone old cory forages half-heartedly, and ground he can still work without hurting the whiskers he reads the world with.
Spread the food across his smaller range
Adjust feeding to a senior corydoras catfish's contracted map. A young school will cross the whole tank floor to a single pile of sinking food; a senior often arrives after the pile is gone or does not make the trip at all. Scatter his sinking foods across two or three patches, with at least one patch beside the cover where he rests, so every bout he does make pays off. Vary which patch gets the richest portion each evening and his foraging keeps a purpose, a small discovery built into each shuffle. Feed after the midwater fish have had their fill, so food actually reaches the floor his exercise happens on.
Soft ground is senior equipment, not decoration
Substrate becomes medical equipment for a senior corydoras catfish. His barbels, the sensory whiskers he digs with, wear and erode more easily in old age, and coarse or sharp gravel that a young cory tolerated can leave a senior with shortened, sensitive barbels that blunt his foraging. Smooth sand he can plunge his face into is the kindest floor for an old fish, and if a full change is impractical, a shallow sand patch over his main foraging area gives him one proper digging field. Add broad leaves at floor level for the rests that now punctuate his bouts, and keep the floor vacuumed, because a senior dragging his belly through waste is prone to skin trouble he once resisted.
Reading a senior cory's slowdown honestly
Expect a senior corydoras catfish to be last out at feeding, first to rest, and content with the school's quieter end. Act when he stops joining bouts altogether, sits apart from the group on open ground, or shows barbels worn to stubs alongside a thinning body. Corys also shoot to the surface for a gulp of air, and a senior doing this far more often than his schoolmates is flagging low oxygen or poor water, not exercising. Test the water, increase aeration, and consult an aquatic veterinarian if the isolation or wasting continues. Because corys decline as a group experience, check whether the whole school has slowed with age before singling out one fish as ill.
The floor plan, written for whoever feeds next
A cory tank's care lives at floor level: which patches get food, where the old fish rests, why the sand patch matters. A feeder who drops one pile at the front and siphons roughly across the digging field undoes all of it in a week. KinsLe's Pet Passport records that floor plan with his school's history in one packet, so a senior corydoras keeps foraging his own ground, at his own pace, under any caretaker.