The bottom is their whole world
Corydoras live on the substrate, shuffling through it in a group, sifting mouthfuls for food, and resting together in a favourite patch of open ground. Their barbels, the sensitive whiskers around the mouth, do the finding, which means the gravel you vacuum is both their dining table and the tool they taste it with. Stress for a cory shows as frantic darting to the surface, a group scattering in all directions, or fish that go still and stop feeding afterwards. Cleaning in a way that lets the group move aside as a group keeps the whole job low-key for them.
Choose the calm moment and the right section
Set out the siphon and bucket, plus conditioned water for the small top-up vacuuming leads to, before you begin. Corydoras are busiest at feeding time and in the evening, so a quiet mid-session moment suits the clean. Decide which portion of the bottom to deep-clean this time, ideally the feeding zone where tablets and pellets crumble into the gravel, and plan to leave the group's resting patch for the next session. Smooth, rounded gravel or sand is the right surface for barbels, and noticing any newly sharp or compacted areas during the clean is useful information for their comfort.
Let the group lead the pace
Start the siphon in an unoccupied stretch and work slowly, pushing the nozzle down so mulm lifts out of the gravel, then stepping it along. As you approach the corys, slow further and let them amble ahead of the tube; curious individuals often turn back to sift the freshly disturbed gravel for exposed food, which is charming but means watching the intake whenever a small body nears it. Avoid sweeping the nozzle sideways through a resting group or dropping it suddenly from above, the two movements most likely to trigger the panicked surface dash. If the group does scatter, hold the siphon still until they resettle on the bottom, then continue or wrap up.
Finish without stripping their table bare
Corydoras benefit from a bottom that is clean but not sterile: vacuumed of rotting waste, yet still holding the fine food particles they sift for between meals. Top up with conditioned water at tank temperature poured in gently, restart the filter, and scatter the day's food over the cleaned area so the group associates the session with a reward. Check barbels in the following days; healthy ones stay long and even, while erosion or redness points to dirty or rough substrate and means the deep-clean rotation should reach the neglected corners more often.
Rotate sections, share the knowledge
A simple rotation, feeding zone this time, resting patch next, filter corner after that, keeps a cory tank consistently clean while any single session stays short and calm. Helpers need the same map, since a well-meaning full-tank blitz is exactly what stresses the group. Leave one favourite resting patch completely untouched each session, because returning to a familiar corner helps the whole group resettle quickly instead of quartering the tank looking for somewhere that still feels like home. Jotting the rotation into KinsLe Care Teams means the person vacuuming the cory tank can mark which section was done and hand the next one cleanly to whoever follows.