An elderly corydoras catfish should be checked over at home once a week, with weighing kept occasional rather than routine. Corydoras live at the bottom, wear bony armour and find their food with delicate barbels, so the senior check happens mostly by watching the floor of the tank, and the scale comes out only when his body shape suggests a trend worth confirming.
The weekly floor-level check for an elderly corydoras
Once a week, watch the senior corydoras forage at feeding time and read the details only this species shows. Barbels come first: an elderly corydoras should keep them long and even, because shortening or fraying barbels point to rough substrate or a floor-level problem that will worsen quietly. Viewed from above, his body should stay broad and rounded through the middle; a senior who looks pinched behind the head while the group stays plump is losing condition.
When weighing an elderly corydoras adds something
Weigh a senior corydoras when the weekly check raises a question the eye cannot settle: a borderline shape change across two or three weeks, a vet's request during treatment follow-up, or a baseline wanted before a diet adjustment. Monthly weighing is the most a healthy elderly corydoras ever needs, and many keepers weigh less often than that, relying on shape and appetite. Skip the scale in any week he is already stressed, newly moved or off his food, because the number will be read against a bad day and the handling will cost an old fish real energy. Treat one reading as a rumour and three readings as a trend; only the trend should change what you do.
How to weigh an armoured bottom-dweller safely
Weigh an elderly corydoras in water, in a smooth container, never lifted in a coarse net where his spines can catch. Set the container of tank water on the scale and zero it, then guide the fish in with a soft net or by sinking the container near him and letting him swim in during a gentle herd. Keep him submerged throughout, because corydoras gulp air at the surface normally but should never be held out of water on their armour. Work smoothly and briefly, note the weight, and tip him back over his sand, watching him settle and give the small tail-flick that means he is oriented.
Records that suit a bottom-dwelling senior
Keep the weekly line short and species-specific: barbel condition, belly shape from above, foraging with the group or alone, resting posture and breathing rate compared with his tankmates. Add the occasional weight and a monthly photograph taken from above at feeding, when he is reliably in the open. Log water results and, for this species, substrate notes too, because a senior corydoras's barbels record the state of the sand or gravel he sifts daily. Compare him against his group and against his own last month, since corydoras age socially and a lone change in one old fish reads differently from a change the whole shoal shares.
Elderly corydoras changes that need a vet
Contact an aquatic veterinarian if an elderly corydoras loses his barbels down to stubs, develops redness or sores on the belly that rests on the substrate, or stops foraging with the group for more than a day. Rapid breathing isolated to him, a persistent list to one side, or visible thinning confirmed across three weights also belong in a consultation rather than in more home watching. Bring the check notes, the weight trend and recent water results; a bottom-dweller's history is mostly written in exactly those records. KinsLe Pet Passport keeps an elderly corydoras catfish's barbel notes, weights and water records in one packet for any vet visit.