How many Bronze Corydoras in a 40 gallon tank?

A 40-gallon (151 L) tank comfortably holds about 11–16 Bronze Corydoras as a single-species display — a conservative range that leaves room for tankmates and a margin for error.

Bronze Corydoras key facts

TankStocking sizes this from a per-species footprint — the territory and waste a single Bronze Corydoras needs in a comfortable display tank — rather than the unreliable "inch per gallon" rule. On that basis a 40-gallon tank comfortably suits about 11–16 Bronze Corydoras. Keep a minimum of 6 — Bronze Corydoras is a social species that suffers in smaller groups. This is a comfortable display range, not a hard ceiling: stocking lighter keeps water quality stable and leaves headroom for tankmates and growth.

TankStocking's bio-load gauge alone would not flag a tank this size as over-stocked until roughly 23 Bronze Corydoras — but that is a model maximum, not the recommended number. It leaves no headroom for water-quality swings, tankmates, or growth, so treat 11–16 as the comfortable target.

They occupy the floor, ask nothing of mid-water fish, and clear the engine against almost every peaceful community species. The few cautions are temperature edges and very large or aggressive tankmates. Keep them in a group of six or more on smooth sand or rounded gravel that protects their barbels.

Want a community rather than a single-species tank? The Bronze Corydoras tank mates guide lists the species the engine clears with Bronze Corydoras.

Keeping Bronze Corydoras well: the detail

Beyond the table — the behaviour, the parameters that actually move the needle, and the mistakes that cost fish. Hobbyist context, not a verdict; the planner above is what judges your plan.

Water parameters in practice

Bronze cories are unfussy on chemistry — neutral to slightly soft or hard, 22–26 °C — but they are fussy about substrate. Smooth sand or rounded gravel is non-negotiable: sharp grains wear away the barbels they use to forage, and an eroded-barbel cory is a starving one. Keep the bottom clean, because that is where they live and feed.

Why Bronze Corydoras behaves the way it does

Corydoras are armoured, shoaling catfish from the soft-bottomed streams and shallows of South America, where they sift sand for food in groups, never alone. The shoaling is safety behaviour, and the constant sifting is how they eat — both explain why a single cory or a pair sits hidden and anxious. They also gulp air at the surface, a normal adaptation to low-oxygen water, not a sign of distress.

Common Bronze Corydoras stocking mistakes

The first mistake is sharp gravel, which quietly destroys their barbels over months. The second is too small a group — fewer than six leaves them shy and inactive. The third is assuming they are a "clean-up crew" that lives on leftovers; they are a fish that needs its own sinking food, not the scraps the others miss.

Early signs something is wrong

Worn-down or missing barbels, a cory that rests with clamped fins, and reddened patches on the belly are the substrate-and-hygiene warning signs. Frantic, repeated dashes to the surface beyond their normal air-gulping suggest poor water quality. A healthy cory group forages busily across the bottom and rests in company, not hidden alone.

How tank size changes the answer

Six is the minimum and they want 20 gallons of floor to forage across. A longer tank beats a taller one — bronze cories use the bottom, so footprint is what counts. Bigger groups of eight or ten in a 29-gallon-plus are noticeably bolder and busier, and they pair naturally with a mid-water school above them.

Stocking in stages: cycle first, then add slowly

The stocking numbers on this page assume one thing the calculator can't do for you: a cycled tank, filled gradually. Even with the volume to spare, adding a full stock at once can outrun the filter bacteria — stage it.

1. Cycle before any fish. Run a fishless cycle — an ammonia source plus the filter — until the tank processes ammonia and nitrite to zero within 24 hours. That typically takes four to six weeks. This is the step that prevents most early losses.
2. Add one group at a time. Introduce a single species or group, then wait a fortnight before the next, testing the water in between. Each addition is a load the filter bacteria have to catch up with.
3. Heaviest waste producers last. Bring in the big, messy fish once the tank is mature and the bacteria are well established, not on day one.
4. Stop short of the limit. The comfortable numbers above leave headroom on purpose. Stocking lighter keeps water quality stable and gives you room to correct mistakes.

Test your real, staged plan in the planner above — it scores the full list against the same welfare engine, whatever order you intend to add fish in.

Common questions

More on stocking Bronze Corydoras

Related guides on TankStocking — each scored by the same welfare engine as the planner.

Stocking numbers are planning estimates — filtration, planting, and maintenance all shift the real ceiling. Cycle the tank and stock gradually. How this estimate works →