Last Updated: June 16, 2026
Few fish bring as much charm to a community aquarium as the Corydoras catfish. These small, armored bottom-dwellers are famous for their endearing “wink,” their constant foraging across the substrate, and their peaceful, social nature. Often called “corys” by hobbyists, they are one of the best beginner-friendly bottom-dwellers available, helping keep the tank floor tidy while schooling together in playful groups. This guide covers everything you need to keep Corydoras healthy and thriving, from tank setup and substrate to diet, tank mates, and health.
Meet the Corydoras Catfish
Corydoras are a large genus of South American freshwater catfish, with well over 150 described species. Popular aquarium types include the bronze cory, peppered cory, panda cory, and the tiny pygmy cory. Most commonly kept species reach about 1.5 to 3 inches in length, though dwarf species stay under an inch and a half. They are covered in bony plates (called scutes) rather than typical scales, which gives them their “armored catfish” nickname.
One of the most important things to understand about corys is that they are schooling fish. They feel secure and behave naturally only when kept in groups of at least six of the same species. A lone cory, or just a pair, will often be shy, stressed, and less active. Keeping a proper school brings out their best behavior, including coordinated foraging and the occasional dash to the surface for a gulp of air, which is completely normal.
Tank Size and Water Parameters
Because corys are active and need company, a school of common-sized species does well in a tank of 20 gallons or larger, while dwarf species can be kept in smaller setups. A longer footprint is more valuable than height, since corys spend their lives along the bottom. If you are planning your first tank, our 20 gallon aquarium setup guide is a great starting point for the right footprint and equipment.
Corydoras are tropical fish that appreciate stable, well-cycled water. Aim for the following ranges:
| Parameter | Recommended Range |
|---|---|
| Temperature | 72-79°F (most species) |
| pH | 6.5-7.5 |
| Hardness (GH) | Soft to moderately hard |
| Ammonia / Nitrite | 0 ppm |
| Nitrate | Below 20-40 ppm |
Always fully cycle your aquarium before adding corys. If you are new to cycling, read our fish tank nitrogen cycle guide and avoid the common pitfall of new tank syndrome. Routine testing with a reliable kit, as explained in our aquarium water testing guide, keeps parameters in the safe zone.
Substrate: Why Sand Matters
If there is one detail that separates thriving corys from struggling ones, it is the substrate. Corydoras have delicate sensory barbels (“whiskers”) around their mouths that they use to sift through the substrate for food. Sharp or coarse gravel can wear down and damage these barbels, leading to infections and a loss of their ability to feed efficiently.
For this reason, soft sand or smooth, rounded fine gravel is strongly recommended. Sand lets corys do what they love most: burrowing their faces in to hunt for morsels. Keep the substrate clean, because waste trapped in the substrate can irritate barbels. Gentle, regular vacuuming during water changes helps. If you are aquascaping, sand also pairs beautifully with carpeting plants like those in our Java moss guide.
Diet and Feeding
Corydoras are omnivorous scavengers, but it is a myth that they survive on leftovers alone. They need their own dedicated food that actually reaches the bottom of the tank. Because they feed at the substrate, slow-sinking foods are essential.
- Sinking pellets and wafers formulated for bottom feeders or catfish
- Frozen or live foods such as bloodworms, daphnia, and brine shrimp for variety and conditioning
- Quality flake that sinks, fed in moderation
- Occasional blanched vegetables
Feed once or twice daily, offering only what they can finish in a few minutes. Make sure faster mid-water fish are not eating everything before it sinks. For broader feeding strategy across a community, see our stocking density and bioload guide to avoid overfeeding and excess waste.
Tank Mates and Temperament
Corydoras are model community citizens. They are peaceful, non-aggressive, and spend their time minding their own business along the bottom. They pair well with small to medium peaceful species that occupy the upper and middle water column, such as neon tetras and harlequin rasboras. Other gentle bottom-dwellers like the kuhli loach can also coexist nicely.
Avoid housing corys with large, aggressive, or territorial fish that may bully or outcompete them. Before mixing species, check temperaments and parameter overlap using our fish compatibility guide.
Health: Scaleless Sensitivity
Corydoras are considered scaleless (their bony plates are not true scales), which makes them more sensitive to certain medications and to salt than many scaled fish. When treating disease, always read product labels carefully, as some treatments containing copper or high doses of certain chemicals can harm catfish. Many keepers dose medications at a reduced level for scaleless fish, following the manufacturer’s guidance.
Maintaining excellent water quality is the best disease prevention. Keep ammonia and nitrite at zero, perform regular water changes, and quarantine new arrivals before adding them to the display. If you do see symptoms, consult our fish disease diagnostic guide and general disease prevention tips before reaching for medication.
Frequently Asked Questions
How many Corydoras should I keep together?
Keep at least six of the same species. Corys are schooling fish that become stressed and reclusive when kept alone or in pairs. Larger groups encourage natural, active foraging behavior.
Why do my Corydoras dash to the surface?
Corydoras can gulp atmospheric air at the surface and absorb oxygen through their intestine. An occasional dash up is completely normal. However, if they are doing it constantly, test your water, as poor water quality or low oxygen may be the cause.
Can I keep Corydoras on gravel instead of sand?
Smooth, fine, rounded gravel can work, but sharp or coarse gravel risks wearing down and damaging their sensitive barbels. Soft sand is the safest and most natural choice for protecting their barbels and supporting their foraging behavior.
Are Corydoras good for beginners?
Yes. They are hardy, peaceful, and adaptable as long as you provide a proper school, soft substrate, stable cycled water, and food that reaches the bottom. They are one of the most beginner-friendly bottom-dwellers in the hobby.
What temperature do Corydoras need?
Most popular species do well between 72 and 79°F. A reliable heater keeps temperatures stable, which is important since fluctuations stress fish and weaken their immune response.
