Corydoras first aid is shaped by how these fish live: on the bottom, in a group, exploring the substrate with delicate barbels. The kit that serves them protects those barbels, keeps the bottom layer oxygenated, and measures the water they actually sit in — which is where waste settles and where problems start.
Water testing aimed at the bottom layer
A liquid test kit leads the corydoras first aid shelf. Corydoras rest in the lowest water in the tank, exactly where uneaten food decays and ammonia concentrates, so a school that suddenly darts to the surface gulping air is often reporting a bottom-layer water problem rather than a fish disease. Test ammonia, nitrite, nitrate, and pH, and draw the sample water from near the substrate for an honest reading. Keep a thermometer in the kit too, and record the school's normal readings on a card so an abnormal result is recognizable at a glance.
A smooth hospital tub, built for barbels
The corydoras quarantine container needs a smooth, bare bottom or a thin layer of fine sand. The barbels around a corydoras' mouth erode on rough gravel and sharp substrate, and a fish whose barbels wear down cannot find food properly afterward — so the hospital tub must never replicate the coarse surfaces that cause the injury. Add a battery air pump with an airstone weighted to sit low, keeping oxygen where the fish are, and a gentle filter if the stay extends. Keep the tub's light dim and add a smooth cave or pipe section, since an exposed corydoras in bare bright water stays stressed.
Soft handling tools only
A soft, fine-mesh net is a first aid supply for corydoras, not a convenience. Their fin spines and barbels snag in coarse mesh, and a panicked extraction can tear a pectoral fin or strip the very barbels the kit exists to protect. Better still for short moves: guide the fish into a submerged cup and lift water and fish together. Pack water conditioner and a dedicated siphon for partial water changes — the standard first response to a bad bottom reading — plus plain towels, because bottom-focused water changes spill more than top-ups do.
Observation notes for a group, not an individual
Corydoras first aid observation tracks the school. Note which fish stop foraging at feeding time, whether surface-gulping is one fish or all of them, and the state of barbels across the group: uniform shortening suggests the substrate or water, while one fish's damage suggests injury. A short log with test readings beside behavior notes separates a tank problem from a fish problem, and that distinction decides whether the response is a water change for everyone or closer attention to a single catfish.
The threshold for professional help
Bring in an aquatic veterinarian when a corydoras stops eating entirely, when barbels erode despite smooth substrate and clean readings, when several fish show redness, sores, or rapid breathing at once, or when one fish cannot stay upright on the bottom. Home supplies stabilize water and reduce stress; they do not resolve everything a school can face. If you find yourself staring at a symptom you cannot place, KinsLe's Kinny is a calm next step — ask for guidance in the moment, work through what to observe, and what you learn stays alongside your corydoras' profile for the follow-up check.