Corydoras join resident fish after quarantine and acclimation
A corydoras catfish meets resident fish only after quarantine and a slow acclimation, never by being tipped straight into the main tank. Keep the new corydoras in a separate small tank for a couple of weeks first, watching them eat, breathe steadily, and school together without clamped fins or white spots. On moving day, float or drip-acclimate them so temperature and water chemistry shift gradually, because bottom-dwelling fish feel a sudden change across their whole body and barbels. Release the corydoras near the substrate with the lights dimmed, ideally in their small group together, so they can settle into the lower layer they will occupy while residents adjust above them.
Why corydoras must arrive as a group, not alone
A single corydoras introduced to resident fish often hides and refuses food, while a group settles within hours. Corydoras are social bottom-feeders that read safety from each other's behaviour, resting in loose clusters and foraging across the substrate together. Adding at least a small school of the same type means no one fish carries the full attention of curious residents, and the group begins its normal shuffling, snuffling routine quickly. That routine is your baseline: a school that fans out to feed at lights-on is comfortable, while fish still frozen under one leaf days later are telling you the resident mix, current, or cover is not working for them.
Watching the first feeds with resident fish
First feeds reveal whether resident fish will let corydoras eat in peace. Corydoras feed at the bottom on sinking food, and faster mid-water residents can strip a meal before a single pellet reaches the substrate, so scatter food at both levels and watch the corydoras' bellies over the first week rather than the surface frenzy. Provide smooth substrate and low hiding places such as rounded caves or dense plant clumps where the school can rest out of any boisterous resident's path. Chasing that ends in a nip, a corydoras repeatedly driven off food, or fish surfacing to gulp air far more than usual all call for more cover, feeding after lights dim, or separating an incompatible resident. Keep a spare low cave free during this period, because a resting spot nobody has claimed yet gives shy newcomers somewhere neutral to regroup.
If a land-based resident pet is part of the picture
A resident cat or dog meets corydoras the same way it meets any tank: through glass, briefly, and with the lid secured. Corydoras startle as a school when a shadow or paw hits the tank, darting together in a way that can fascinate a watching pet into pawing again, so keep early viewings short and reward the resident pet for settling away from the stand. Because corydoras rest at the bottom, they are less visible than surface fish, and that lower profile usually helps resident pets lose interest quickly. Make sure the stand is stable and cords are tucked away, since an excited larger pet bumping the cabinet stresses the whole tank, not just the newcomers. With KinsLe and Care Teams, quarantine water checks, acclimation timing, and those first supervised viewings can each have an owner, keeping the introduction orderly.