Corydoras Catfish

Corydoras are peaceful armored bottom dwellers that only thrive in groups of 6+ on sand—not gravel that shreds their barbels. They are not free cleanup crew: feed sinking foods daily or they starve while looking “busy.” Soft water, gentle flow, and a real school turn them into the most entertaining community catfish you can keep.

Who This Fish Is For

Corydoras are for aquarists who will keep a school on sand and feed the bottom on purpose. If you want lively, peaceful catfish that sift substrate all day and ignore almost every community fish, corys are the default answer.

They are the wrong buy if you plan three “cleaners” on sharp gravel, a lone specimen “to eat leftovers,” or a tank with oscars and other large predators. Over 160 species exist—from 1” pygmies to ~3” standards—but the rules barely change: sand, six or more, sinking food. Species pages for favorites: bronze cory, panda cory, sterbai cory, pygmy cory.

Care Snapshot

Spec	Value
Adult size	~1–3” depending on species
Minimum tank	10 gal (pygmies); 20 gal (standard species schools)
Recommended	20–40 gal for a proper group
Temperature	72–78°F (Sterbai warmer; peppered cooler-tolerant)
pH / hardness	6.0–7.5, soft to moderate
Temperament	Peaceful, social
Group size	6 minimum; 8–10+ better
Substrate	Sand (or very smooth rounded fine gravel)
Diet	Sinking pellets/wafers + frozen; not leftover flakes
Lifespan	5–10 years

Plan numbers with the stocking guide and tools.

Tank Setup

Substrate is non-negotiable. Corys shove sensitive barbels into the bottom constantly. Fine sand (aquarium sand, rinsed play sand, pool filter sand) is the gold standard. Smooth, rounded 2–3 mm gravel can work; crushed sharp gravel causes barbel erosion, infection, and starvation because they cannot forage. Bare glass is stressful. If barbels are already stubs, switch to sand—regrowth is slow but possible.

Tank size by type:

• Pygmy / dwarf (C. pygmaeus, habrosus, hastatus): 10+ gallons, groups of 8–10+
• Standard (bronze, peppered, panda, sterbai, julii-type): 20+ gallons for six; 29–40 better
• Larger Brochis-type: 30–55 gallons

Filtration: Gentle flow. Sponge filters excel. Pre-filter sponges on intakes—corys can pin on bare intakes. Moderate oxygenation; they gulp air at the surface as normal intestinal breathing, not automatic distress.

Aquascape: Open sand runways for foraging, plus caves, wood, leaf litter, and plants (crypts, Anubias, Java fern, floats). Dim corners reduce shyness. Leave at least one clear “highway” of sand across the front so you can watch the school work.

Popular species pick: Bronze and peppered for bulletproof beginners; panda for planted show tanks; Sterbai for warmer community tanks (angels, discus-range heat); pygmies for nano and shrimp tanks (they often swim midwater more than standard corys).

Quarantine new fish; corys ship poorly and can import parasites: quarantine setup. Full system: complete aquarium setup and substrate guide.

Water Parameters

• Temperature: 72–78°F for most; research species (e.g. Sterbai often 75–82°F)
• pH: 6.0–7.5; stability first
• Hardness: Soft to moderate preferred
• Ammonia / nitrite: 0 ppm—highly sensitive
• Nitrate: Keep under ~30 ppm
• Meds: Treated as scaleless for many drugs (half dose common); avoid copper

Weekly 25–30% water changes, careful vacuuming so you do not blast the school. Cycle fully before adding: how to cycle a new aquarium.

Diet and Feeding

They are not tank cleaners. Leftover flakes that reach the sand are not a diet. Midwater fish intercept food first.

Daily: Sinking pellets or wafers formulated for bottom feeders (after lights out or after other fish finish). Enough that food is still findable for 20–30 minutes.

2–3× weekly: Frozen bloodworms, brine shrimp, blackworms, daphnia.

Optional: Blanched zucchini/cucumber, algae wafers for plant matter—not as their only “algae eater” role.

Health check: Rounded bellies, active sifting, intact barbels. Sunken gut, pale color, or lethargy = underfed or sick. Target-feed with a dish on the sand if competition is heavy. Nutrition overview: feeding and nutrition.

Temperament and Tank Mates

Among the most peaceful fish sold. They school, rest in piles, “blink” by rotating eyes, and dash to the surface together to gulp air—normal and entertaining.

Group size: 6+ same species preferred for tight schooling. Mixed Corydoras species coexist but may not form one tight school. Singles and pairs hide and stress. In a proper group you should see coordinated foraging, resting piles, and synchronized surface dashes—those behaviors are the point of keeping them.

Great mates: Neon and other small tetras, rasboras, livebearers, dwarf gouramis, angelfish in larger tanks, bettas in 15+ gallons with space, bristlenose pleco, adult cherry shrimp (babies may be snacks).

Avoid: Oscars, large predatory cichlids, anything that can swallow a cory, hyper fin-nippers in tight quarters. Goldfish pairings are a poor default—temperature and mess levels rarely line up long-term.

Handling note: Dorsal and pectoral spines can lock and sting like a bee. Scoop with a container, not a fine net that tangles spines; double-bag for transport. The armor and venom are why many large fish learn to leave them alone—but do not test that with a hungry oscar.

Breeding (bonus): Many species spawn after a large, cooler water change (simulating rain). Eggs go on glass and plants; parents do not care for fry. Move eggs or adults if you want survival.

Compatibility: choosing compatible tank mates.

Common Mistakes

1. Sharp gravel. #1 cause of barbel loss and chronic infection.
2. Keeping 2–3 as “cleanup crew.” Need 6+ and real food.
3. Assuming leftovers feed them. They starve while the glass still looks clean.
4. Strong intakes without guards. Injury or death on the filter.
5. Copper meds and full-strength ich treatments. Scaleless-sensitive physiology.
6. Misreading air gulps as drowning. Occasional surface dashes are normal; constant gasping + poor tests is not.
7. Pygmies in a bare 5-gallon with no cover. Small species still need schools, biofilm-rich plants, and calm water.

Frequently Asked Questions

How many Corydoras should I keep?

Minimum 6, preferably 8–10+. Smaller groups stay shy and stressed.

Sand or gravel?

Sand. Only very smooth, fine, rounded gravel is a second choice. Never sharp crushed gravel.

Why do they shoot to the surface?

They breathe atmospheric air through a modified gut. Group dashes are normal. Constant gasping warrants an immediate water test.

Do Corydoras eat algae or waste?

They pick at leftovers and some biofilm; they are not algae eaters or poop cleaners. Feed sinking foods daily.

Can different Corydoras species live together?

Yes peacefully. For the best schooling display, keep one species in larger numbers.

Can they live in a 10-gallon?

Pygmy types in a group, yes. Standard bronze/panda/sterbai schools need 20+ gallons.

Why are their barbels disappearing?

Rough substrate and/or dirty substrate bacteria. Move to sand and improve water quality immediately.

Do they work with shrimp and bettas?

Usually with adult shrimp and many bettas in roomy, planted tanks—monitor individual temperament. See cherry shrimp and betta behavior notes in the tank mate guide.

Related Resources

• Complete aquarium setup
• How to cycle a new aquarium
• Aquarium substrate guide
• Stocking guide
• Choosing compatible tank mates
• Quarantine tank setup
• Feeding and nutrition
• Bronze cory, panda cory, sterbai cory, julii cory, peppered corydoras, pygmy cory, albino corydoras
• Bristlenose pleco, angelfish
• Tools