Look at a beginner's tank for thirty seconds and you can usually spot what is missing. The middle is busy, the top has a few fish patrolling for food, and the bottom third — the largest single volume of water in the tank — is empty. Nothing lives there. Nothing uses it.
That is a waste of the space you paid for, and it is also a missed opportunity to make the tank look busier without adding a single fish to the crowded upper layers. Bottom dwellers occupy a stratum nobody else wants. Stocked properly, they are close to free space in a way no other addition is.
But "stocked properly" is doing a lot of work in that sentence, because bottom fish are also the group most often bought for entirely the wrong reason.
They are not a cleaning crew
Let us kill this one first. Corydoras are not janitors. They will not eat your uneaten food off the substrate, they will not consume fish waste, and they will not keep your gravel clean. That is not what they are.
They are omnivorous foragers with a specific diet requirement that must be fed deliberately, every day, the same way you feed everything else. A shop that sells you corydoras as a solution to a dirty substrate has sold you a fish that will slowly starve while your substrate stays exactly as dirty as it was. The actual solution to a dirty substrate is a gravel vacuum and a regular water change.
Buy bottom dwellers because they are interesting, active, social animals that use a part of the tank nothing else does. That is a good reason. "It will clean up" is not.
Substrate is not optional, and it is not negotiable
This is the single biggest thing to get right, and it is a decision you make before the fish arrive, because changing substrate in a stocked tank is a genuinely miserable job.
Corydoras feed by sifting. They push their snout into soft substrate, take in a mouthful, filter it through the gills and blow out the rest. They are equipped for this with a pair of sensory barbels around the mouth — the little whiskers — which are soft tissue and are the whole reason the fish can find food it cannot see.
Put that fish on sharp gravel and the barbels abrade. Put it on gravel that traps waste, and bacteria get into the abrasions. Within a few months you have a cory with stumps instead of barbels, permanently unable to forage properly. It is extremely common and it is entirely preventable: smooth sand, or very fine rounded gravel, and nothing else. Our substrate guide covers the options and what to look for; for corydoras the answer is the sand end of that article.
Bare-bottom tanks are worse, not better. A cory on glass cannot perform the behaviour its entire body plan is built around.
Six is a minimum, not a target
Bottom dwellers are shoaling animals and a pair is not a shoal. Two corydoras in a tank spend most of their time hidden and stressed. Six of the same species spend the day out in the open, sifting in a loose group, occasionally darting around together for no obvious reason. It is a completely different animal.
Note "of the same species". Six bronze corys shoal. Two bronze, two panda and two albino do not — they are three inadequate groups sharing a tank, and while they will tolerate it, you lose the behaviour you bought them for. Pick one species and commit to it. If you want two species, you need a group of each, which means the tank has to be big enough. The stocking guide is worth a look before you decide.
Which species actually work here
This is where UAE conditions change the standard advice, and it matters more than most guides let on. Corydoras species come from different altitudes and different water temperatures, and some of the most commonly sold ones are cool-water fish.
- Corydoras sterbai — the one to buy if your tank runs warm, which in this country it does. Sterbai are comfortable at temperatures that stress other corys, which is why they are the standard choice for discus keepers. Slightly more expensive, worth it.
- Corydoras aeneus (bronze and albino) — the hardiest and most adaptable of the commonly available species, and the easiest to find locally. A safe default.
- Corydoras paleatus (peppered) — a genuinely cool-water species. It does best well below what a Dubai flat sits at in July. Widely sold, frequently a mistake here.
- Corydoras panda — attractive and popular, also prefers the cooler end, and is noticeably more delicate as a shipped fish. Not a first cory.
- Corydoras trilineatus / julii — usually sold interchangeably, mid-range in hardiness, fine in a stable tank.
If you take one thing from this section: sterbai for a warm tank, bronze for a beginner tank, and think twice about peppered and panda.
What about hard water?
Honest answer: corydoras are soft-water fish in the wild, and our tap water is the opposite of that. In practice, commercially bred corydoras — which is essentially all of them on the market — have been raised for many generations in whatever the farm's water was, and adapt to hard alkaline water without much drama.
They are not as effortlessly at home here as guppies and other livebearers, which genuinely want this water. But they are not a fight either. Do not chase pH downwards to suit them — stability matters far more than the number, for the same reasons set out in the pH article. Check what is actually coming out of your tap first: our tap water guide has the detail.
The surface gulping thing — and when it is a problem
Corydoras have a modified intestine that absorbs atmospheric oxygen. A cory will periodically shoot up to the surface, take a gulp of air and drop back down. This is completely normal behaviour and not a sign of anything wrong. Most new keepers panic the first time they see it.
What is not normal is constant trips, one after another, or a cory that hangs at the surface rather than returning to the bottom. That means the water genuinely lacks oxygen, and in a UAE summer that is a real risk: warm water holds measurably less dissolved oxygen, and the bottom of the tank is where it runs out first. Our guide to oxygen and air pumps explains why, and the summer cooling guide covers the other half of the problem. Bottom fish are your early warning system for both.
Feeding them properly
Sinking food, after lights out or at least after the upper-level fish have eaten. Sinking wafers, catfish pellets, frozen bloodworm and frozen daphnia are all good. Flake does not count — it is gone before it reaches the bottom.
The classic failure is a tank where the guppies and tetras intercept everything and the corys quietly decline over months. If your bottom fish look thin or their bellies have gone concave, they are not getting fed, regardless of how much food goes in the tank. Feed them directly and watch that they actually get it. The feeding guide covers portion sizes and the seasonal adjustment for summer.
The other bottom dwellers worth knowing
Kuhli loaches. Eel-shaped, nocturnal, and completely dependent on sand plus dense hiding places. Keep six or more or you will never see them. Charming when they settle in, invisible if the tank is bare.
Bristlenose pleco (Ancistrus). The sensible pleco. Stays at a manageable adult size, genuinely does eat algae, and needs driftwood in the tank to rasp on — see the driftwood and rock guide. Covered in more detail alongside the alternatives in our algae eater article.
Nerite snails. Bottom and glass, hard-water lovers, no reproduction in freshwater. Close to a free win.
What to avoid: the common pleco, which is sold at eight centimetres and reaches forty-five; and the Chinese algae eater, which becomes territorial with age and starts rasping the slime coat off slow-moving fish. Neither belongs in a normal home tank.
Tank, tankmates and settling in
A 60 L tank is a realistic floor for a group of six corydoras plus a modest community above them, and floor space matters more than height for bottom fish — a long, shallow tank beats a tall one of the same volume. The tank size guide makes the case.
They suit almost any peaceful community: livebearers, tetras, rasboras, and shrimp in a planted tank. They are not defenceless — corydoras have locking pectoral spines — but they are non-aggressive and should not be housed with anything that will harass them. The compatibility guide has the full picture.
Filtration should be reasonably gentle and the tank should be fully cycled first — filtration basics and the cycling guide both apply. Corydoras are notably sensitive to nitrite and to dissolved medications, particularly anything copper-based, so read your test kit properly before reaching for a treatment.
They also ship badly. Bottom fish arrive stressed more often than mid-water fish do, so acclimatise slowly and put them through proper quarantine. And dechlorinate every drop of new water — the conditioner guide explains what the products actually do.
Quick answers
Can I keep just two corydoras? You can. They will be stressed and mostly hidden, and you will not see the behaviour that makes them worth keeping. Six minimum.
Mine keep swimming to the surface — is something wrong? Occasional trips are normal air-gulping. Constant trips or hanging at the surface mean low oxygen. Check temperature and increase surface agitation.
Can I keep corydoras on gravel? Only if it is fine and genuinely rounded. Standard aquarium gravel damages barbels over months. Sand is the safe answer.
Why are the whiskers gone? Abrasive or dirty substrate, usually both. The damage is often permanent. Fix the substrate and improve maintenance.
Do they need a heater? Not usually in summer. In winter, yes — to prevent the day-night swing rather than to add heat. See the heater guide.
The bottom line
Bottom dwellers are the cheapest way to make a tank feel complete, and the easiest group to get wrong for reasons that have nothing to do with the fish. Give them sand, give them a group, give them their own food, and pick a species suited to a warm tank rather than whatever was in the shop that day.
If you are planting the tank as well, note that the plants that do best in our hard water are also the ones that tolerate a cory constantly digging around their roots — our hard-water plant guide covers which species those are. And if you are still building the stock list, the beginner fish guide puts the bottom layer in context with everything above it. If things have already gone wrong, start here.