Good corydoras care comes down to four things that beginners skip: company of their own species, a soft bottom they can forage over, food that actually reaches the floor of the tank, and a water temperature that matches the species you bought. "Cory" is not one fish. It is a large group of small South American catfish with different needs. The most common beginner setup, two corys bought to "clean the bottom", fails on at least two of those four counts before the fish are even in the water.
My name is Hossain, and I run this site on one rule: if I cannot tell you why, I do not tell you to do it. So below, every recommendation comes with its reason and, where a number is involved, the source it came from.
What Corydoras Actually Are
Corydoras belong to the armored catfish family, Callichthyidae. The University of Florida's extension circular Freshwater Ornamental Fish Commonly Cultured in Florida (Hill and Yanong, UF/IFAS, which I read on September 27, 2026) describes the family as about 224 species in eight genera, mostly small fish under 100 mm (4 in). It also records three facts that matter more for your tank than any care sheet shortcut:
- Corydoras can breathe air. They dart to the surface, gulp, and absorb oxygen from that bubble in the gut.
- They eat worms, insect larvae and detritus from the bottom.
- They spawn in groups, and their sticky eggs get no parental care.
Notice what is missing from that list: "cleans the tank". Eating detritus is not the same as removing waste. Everything a cory eats comes back out as waste, and it all ends up as ammonia that your filter bacteria have to process.
One more thing worth knowing if you look corys up yourself: scientists have been reorganizing this group. FishBase now files the peppered cory under the name Hoplisoma paleatum and the bronze cory under Osteogaster aenea. If a search for the old name turns up a new one, you are still looking at the same fish.
Why "Two to Clean the Bottom" Is the Wrong Start
The question I hear most is some version of "I got two to clean the bottom. Is that how it works?" It is not, for two separate reasons.
They are not a cleaning crew. A cory will pick through leftover food, but it cannot eat a mess away. Uneaten food and fish waste still break down into ammonia, and the only things that deal with that are a cycled filter, water changes and a gravel vacuum. If you are relying on corys to keep the substrate clean, you are also relying on them to eat food that is going bad, which is not a diet. My guide to how much substrate to actually clean with a gravel vacuum covers what the bottom of a tank really needs.
Two is not a group. Corydoras are social fish. FishBase's aquarium notes for both the bronze and the peppered cory say to keep them "in groups of 5 or more individuals", and its entry for the bronze cory notes that adults in the wild stay in schools of 20 to 30. I read both entries on September 27, 2026. A pair or a single cory is a fish living without the thing its behavior is built around, and the usual result is a fish that hides, forages less and is easier to stress.
Keep the group to one species where you can. Different cory species will sometimes mix, but a fish that looks similar is not always the same kind of company, and as the next section shows, "similar looking" can also mean "different temperature".
Corydoras Care Starts With Knowing Your Species
This is the need that gets skipped most, and it is where the "tropical community fish" label does real harm. Two of the most common corys in the hobby come from very different water. Here is what FishBase records for each (entries read September 27, 2026):
| Species (common name) | Current FishBase name | Max length recorded | Temperature range recorded |
|---|---|---|---|
| Peppered cory | Hoplisoma paleatum | 6.6 cm SL (male), 7.1 cm SL (female) | 18 to 23 °C (about 64 to 73 °F) |
| Bronze cory | Osteogaster aenea (formerly Corydoras aeneus) | 7.5 cm SL | 25 to 28 °C (about 77 to 82 °F) |
Those two ranges do not overlap at all. The peppered cory comes from Argentina, Brazil and Uruguay, according to FishBase, and its recorded range sits cooler than many tropical tanks are kept. The bronze cory's recorded range sits warmer.
These are ranges recorded for the species, not a promise about any individual fish. Farm-raised corys may tolerate conditions outside them, and I will not tell you a single number is "safe". The practical point is simpler: before you buy, find out which species you are actually looking at, look it up, and check that its range fits the tank you already run. If you want the reasoning behind picking a temperature for a mixed tank, I go through it in why "tropical" is not one number.
I also cannot give you a lifespan figure I trust. Care sheets quote wildly different numbers, and I have not found a primary source I would stand behind, so I would rather say nothing than give you a number you might plan around.
The Bottom: Substrate and Barbels
Corys feed with their barbels, the whisker-like feelers around the mouth, pushing their faces into the substrate to find food. FishBase describes the bronze cory's natural habitat as mostly quiet, shallow waters with soft bottoms. That is the environment their feeding style is built for.
In a tank, that means:
- Smooth sand or fine, rounded gravel. This lets them forage the way they are built to.
- A substrate that is kept clean. A soft bottom full of rotting food is worse than a coarse one that is clean.
- Open foraging space. A floor completely covered in rock work or décor leaves them nowhere to search.
Hobbyists argue about why corys sometimes lose or wear down their barbels. Some blame sharp gravel, others blame dirty substrate and poor water quality. I have not found a controlled study that settles it, so my advice covers both: choose a smooth substrate and keep it clean. If barbels are already wearing away, that is worth raising with an aquatic veterinarian rather than guessing, because the cause matters for what you do next.
Air: Why Corys Dash to the Surface
A cory shooting up to the surface, gulping and diving back down alarms many new owners. It is normal. UF/IFAS describes this air breathing for the whole genus, and FishBase's entry for the bronze cory records that they take air anywhere from 1 to 45 times per hour.
Two things follow from that:
- Keep the path to the surface open. A tank sealed with floating plants from edge to edge, or a very tall tank with nothing to rest on partway up, makes that trip harder.
- Do not confuse gulping with gasping. One cory making quick trips up and down is behaving normally. Several fish of different species hanging at the surface is a different situation, and it points to a water or oxygen problem rather than cory behavior.
Food That Actually Reaches Them
In a community tank, corys often eat last. Flakes are taken at the surface by faster fish, and by the time anything reaches the bottom it has been picked over. Corys that "should be fine on leftovers" are often underfed.
What works:
- Sinking foods, such as sinking pellets or wafers, that reach the bottom intact.
- Watching them eat. If you cannot see your corys eating, you do not know that they are.
- Feeding enough without overfeeding. Anything they do not find becomes ammonia.
Their natural diet, as UF/IFAS describes it, is worms, insect larvae and detritus, so a mix of sinking prepared foods and frozen or live worm-type foods gets closer to that than flakes alone. For portion sizes, my guide to what a "pinch" of food actually means applies here too.
When to Add Corys to a Tank
Corys do best in a tank that has finished cycling and has been running steadily for a while, not one that was set up last week. They spend their lives with their faces in the substrate, which is where waste collects, so an unsettled tank hits them directly.
Two habits help:
- Add them to a cycled, stable tank, and add them as a group rather than one or two at a time over months.
- Quarantine new arrivals. A separate tank for a few weeks lets you spot problems before they reach your main tank. I explain the reasoning in why quarantine is the cheapest insurance in the hobby.
Other Bottom Dwellers: The Same Questions Apply
Corys are the most common bottom dwellers in beginner tanks, but loaches, small plecos and other catfish get bought for the same reason: "something to clean the bottom". The same four questions apply to every one of them before you buy:
- How big does it get as an adult? Some fish sold small grow far larger.
- Does it need a group of its own kind?
- What temperature and water does the species come from?
- What does it actually eat, and will that food reach it?
A species database such as FishBase records maximum length, temperature range and aquarium notes for most fish sold in stores. If you cannot answer those four questions, wait until you can. The fish will still be there.
When Something Looks Wrong
If your corys stop foraging, hide constantly, lose color, show red or damaged barbels, or several fish are affected at once, test your water first, because corys live right where waste collects. If the water checks out and the problem continues, contact an aquatic veterinarian. I will not suggest a treatment from a description, because the same symptom can have several causes, and the wrong treatment can be harder on the fish than the problem.
Frequently Asked Questions
How many corydoras should I keep together?
FishBase's aquarium notes for the common species say groups of 5 or more individuals, and wild bronze corys are recorded living in schools of 20 to 30. Two corys is not a group. Keep a group of one species where you can.
Do corydoras clean the tank?
No. They eat leftover food and detritus, but everything they eat comes back out as waste. They do not replace water changes, gravel vacuuming or a cycled filter.
Why do my corydoras swim to the surface?
Corydoras breathe air. They gulp at the surface and absorb oxygen in the gut, which is normal. If several fish of different species are hanging at the surface, that points to a water or oxygen problem, not cory behavior.
What temperature do corydoras need?
It depends on the species. FishBase records 18 to 23 °C for the peppered cory and 25 to 28 °C for the bronze cory, ranges that do not overlap. Identify your species and check its entry before choosing a temperature.
Is sand necessary for corydoras?
Sand or smooth, fine gravel suits how they feed, since they forage with their barbels in the substrate. Whatever you choose, keeping it clean matters just as much.