How many corydoras should I keep together?

Six minimum, same species, ten-plus ideal. A single ' Cleanup crew' cory is the saddest fish in the hobby: solitary corydoras hide constantly and stop feeding normally. Many species do fine split between two species at 6+ each.

Do corydoras need sand instead of gravel?

Smooth, rounded gravel of fine-to-medium size or sand — corydoras vacuum the substrate with delicate barbels that abrade on sharp edges, and wounds invite bacterial infection. Sharp new gravel is one of the most common self-inflicted cory problems.

Why is my cory darting to the surface?

Occasional air gulps are normal — corydoras swallow air and absorb gut oxygen. frantic repeated darting usually means low oxygen or poor water; test ammonia, nitrite and temperature and add surface agitation.

Why did my corydoras die overnight?

Corydoras are more sensitive than tankmates to the invisible killers: ammonia spikes, low oxygen, and copper or medications in dosed tanks. They often show it first — an overnight loss means test the whole panel and review anything added to the water.

Corydoras Care: The Floor Crew That Needs Real Care

Last updated: November 2026

Corydoras — corys — are the hobby's best personality fish: armored, whiskered, comical vacuum cleaners that thrive in noisy crowds. They're also sold as solo "clean-up crew" accessories for bowls, which is how they earn a reputation for "dying suddenly." Truth: corydoras are social, air-breathing, substrate-tending South American fish with three non-negotiables — groups of six or more, smooth substrate, and clean floors. Meet those and they live 10–15 years; ignore them and the barbels, skin, and oxygen all tell on you first.

Quick specs

Item	Requirement
Minimum tank	10 gal (footprint-focused) for small species like pygmy corys; 20 gal for bronze/peppered/sterbai groups
Group size	6 minimum same-species; 10+ ideal; can split 6+6 across two species
Temperature	72–79 °F / 22–26 °C; most common species tolerate the low 80s briefly, not as a norm
Water	pH 6.0–8.0 by species; ammonia 0, nitrite 0, nitrate <40 — corys are dirt-floor fish, so floor hygiene is everything
Substrate	Sand or smooth rounded fine gravel — sharp edges cut barbels
Adult size	1–3 in / 2.5–7 cm depending on species
Lifespan	10–15 years, often longer
Diet	Sinking micro-pellets/wafers + frozen bloodworms/daphnia; floor food, not leftovers

Tank, substrate, and why floors decide cory health

Corys live with their face in the substrate all day, so the floor is their health. Sand or rounded gravel only — test new gravel by dragging a pantyhose over it; if it snags, it shreds barbels, and abraded barbels seed the bacterial skin infections below. The second floor truth: they eat whatever sinks, so uneaten tropical-fish food rotting on the substrate foules their water first. Vacuum the floor at every weekly 25–40% change and feed sinking foods sized so they're cleaned up in under two minutes. Tank size is about footprint: a 20-long beats a 20-tall for groups. Add cover — wood, clumps of plants — because corys are crepuscular and bolder in a half-shaded room. They gulp air at the surface as normal gut-oxygen backup; make sure the surface isn't sealed under a lid film of biofilm (break the surface with the outflow).

Water parameters and temperature honesty

Ammonia and nitrite at 0 ppm is not optional — corys bottom-feed through any toxin that rises from the substrate and their skin shows it as red patches and fuzz first. Nitrate under 40. Temperature: most common species (bronze, peppered, sterbai) live happily 72–79 °F / 22–26 °C; they can share tropical tanks in the upper 70s fine, but permanent rooms above 82 °F / 28 °C shorten lives and raise oxygen risk. One nuance breeders swear by: a 2–3 °F weekly cool change (a small bucket of slightly cooler fresh water) mimics rainy season and triggers breeding behavior — also a good health barometer, because only comfortable corys perform it.

Grouping and tankmates

Single corydoras are chronically stressed corydoras: six-plus of one species in 20 gallons is the standard, two six-fish species is a bigger-tank luxury. Ideal roommates mirror their temperament: tetras, small rasboras, gouramis, and peaceful community fish — and nothing that treats a bottom-dweller as a snack. Angelfish and large cichlids may eat or intimidate them; and remember many cory species are themselves too big to share with big-mouth fish. Avoid aggressive substrate-diggers (large loaches) that stir sharp debris across their face.

Common corydoras illnesses

Illness	Tells	Guide / action
Barbel rot	Shortened, frayed, discolored whiskers; usually sharp substrate + old water	Fix substrate/water; antibacterial per label if spreading; mild cases re-grow when floor is fixed
Bacterial skin infection	Red patches, white fuzz, red streaks on body	Streaks & sores protocol — water change is the backbone
Oxygen stress	Frantic surface darting, gasping at dawn	Gasping guide — airstone now, test water next
Ich / costia	Salt grains or grey sheen after cold dips	Not-ich guide — corys are scaleless-sensitive: halve harsh med doses or avoid formalin/malachite blends
Bloat/constipation	Puffed belly after only dry foods	Fasting + shelled pea; see swim bladder page

Scaleless caution that saves lives: corys lack protective scales, making them the canary for copper medications, strong formalin mixes, and salt-heavy protocols. When medicating a shared tank, dose for the scaleless resident — halve harsh product doses per label guidance or move affected fish to a hospital tank. Many "corys died after treatment" stories are dosing stories.

Prevention

Six-plus same-species group; sand or tested-smooth gravel; weekly floor vacuum.
Ammonia 0 / nitrite 0 / nitrate <40, verified with a liquid kit (kit guide).
Sinking food at measured portions; don't trust them to scavenge scraps — underfed corys thin out silently.
Quarantine 2–4 weeks — corys import ich, costia, and internal worms more than they export anything else.
Dose medications to the cory in the room, not the tetras.

FAQs

How many corydoras together?

Six of one species minimum; ten-plus shows their real personality. The "one cory per tank" sales pitch creates months of hiding and wasting.

Sand or gravel?

Either, if smooth. Sand is easiest on barbels; sharp gravel cuts them and opens infection. Test with pantyhose before buying.

Why do my corys dart to the surface?

Occasional air gulps are normal anatomy. Frantic repeated runs mean oxygen or water trouble — test the panel and add surface agitation.

Can corys share a tank with bettas/angels?

Often fine with a calm betta in 10+ planted gallons; angelfish are riskier (mouth-size and competition). Judge by feeding behavior and hiding patterns, and separate on any sign of chasing.

Severe cases: consult an aquatic-experienced vet where available.