The Best Bottom-Dweller Fish for a Planted Tank

A corydoras (Corydoras aeneus) is not a tank vacuum. Half the reason people buy a bottom fish is wrong: it does not let you skip a water change or clean up after overfeeding. It forages the leftover food a mid-water school misses, and stocked as a cleanup excuse it starves on a bare gravel bed while the real waste rots down in the substrate.

The other half of the reason is right. A bottom group works the lowest level of a planted tank, turns over the top of the substrate, and eats sinking food before it fouls, which does keep a tank cleaner. The trick is choosing the ones suited to a planted community and giving them the sand, the group, and the cover they actually need.

The short version

• A bottom-dweller forages leftover food and grazes the substrate; it does not replace feeding or water changes.
• The four that suit a planted tank: bronze corydoras (Corydoras aeneus), pygmy corydoras (Corydoras pygmaeus), kuhli loach (Pangio kuhlii), and otocinclus (Otocinclus sp.).
• Corydoras need smooth sand, not sharp gravel, which wears their barbels down within a month or two.
• Every one of them is a schooling fish: corydoras in 6 or more, pygmy in 8, kuhli in 5, otocinclus in 6.
• Otocinclus is the trap: it only survives in a tank over three months old with a steady algae film, or it starves.

What a bottom-dweller actually does

A bottom fish forages, and foraging is not filtering. A corydoras (Corydoras aeneus) roots through the top layer of sand for food that sank past the mid-water fish, a kuhli loach burrows and works leaf litter at night, and an otocinclus rasps biofilm and soft algae off leaves and glass. All of that keeps the lowest level of the tank turned over, but none of it removes the dissolved waste a filter and a water change handle.

Substrate is the detail that decides whether a bottom fish thrives or slowly wears out. A corydoras and a kuhli loach both want smooth sand they can sift and burrow into, not sharp gravel, because gravel grinds down the barbels a cory feeds with. Fine sand at the bottom, with some leaf litter and caves for cover, is the setup all four of these fish want.

The four that work

Every number here is copied from the compatibility database, so you can check the overlap with your tank before you stock.

Fish	Latin name	Temp	pH	Hardness (dGH)	Adult size	Group	Min tank
Bronze corydoras	Corydoras aeneus	72 to 79 F	6.0 to 7.5	2 to 12	2.5 in	6+	20 gal
Pygmy corydoras	Corydoras pygmaeus	72 to 79 F	6.0 to 7.5	2 to 12	1 in	8+	10 gal
Kuhli loach	Pangio kuhlii	73 to 83 F	5.5 to 7.0	3 to 10	3.5 in	5+	20 gal
Otocinclus	Otocinclus sp.	72 to 79 F	6.0 to 7.5	4 to 15	1.5 in	6+	10 gal

All four share the soft-to-medium, warm water a low-tech planted tank runs, roughly 73 to 79 F and GH 4 to 10, so any of them slots into the same community. The difference is footprint and habit: the corydoras and kuhli want a 20-gallon floor, while the pygmy corydoras and otocinclus fit a planted 10-gallon.

Corydoras: the workhorse of the bottom

The bronze corydoras is the standard bottom fish for a reason: peaceful, hardy, active by day, and endlessly busy sifting the sand in a group. Keep six or more (they get visibly stressed in smaller numbers), give them smooth sand, and a 20-gallon footprint, and they work the floor of a community all day. At 2.5 inches they are the right size for a mid-size tank.

For a 10-gallon, the pygmy corydoras is the answer. It stays at 1 inch, schools in mid-water as much as on the bottom, and is safe with an adult cherry shrimp colony. Keep eight or more, because a pygmy cory in a small group hides in the plants and you never see it. Both corydoras want the same 72 to 79 F, soft-to-medium water.

Kuhli loach: the night shift

A kuhli loach is the eel-shaped bottom fish that works the floor after the lights go out. It hides by day and forages at night through sand and leaf litter, so in a bright, open tank with no cover you will think it vanished. Keep five or more, give it caves and litter, and it comes out far more, sometimes even in daylight.

It wants soft, warm water (73 to 83 F, pH 5.5 to 7.0, GH 3 to 10) and fine sand it can burrow into, so it suits a soft-water planted community better than a hard one. At 3.5 inches it needs a 20-gallon footprint. It is peaceful with everything, including adult shrimp, though very small newborn shrimp are fair game to any bottom forager.

Otocinclus: the algae specialist, mature tanks only

An otocinclus is a true algae-eater that never harms a plant and stays under 2 inches, which makes it the best small algae grazer for a planted tank. It works the leaves and glass a nerite snail cannot reach into. In the right tank it is one of the most useful fish you can add.

The condition is the whole point: it eats biofilm and soft algae, and a new tank has almost none, so an otocinclus added in the first month slowly starves. Only add it to a tank that has run three or more months and grows a steady algae film, and buy six, because they are social and ship stressed. This is the one bottom fish where patience is the difference between it living and dying.

The honest part: singles, barbels, and starvation

The most common bottom-fish failure is buying one. Every fish here is a schooling or social animal, and a lone corydoras, a single kuhli, or a pair of otocinclus lives stressed, hides constantly, and often fades within weeks. Buy the group (6 corydoras, 8 pygmy, 5 kuhli, 6 otocinclus) or do not buy the fish.

The second failure is substrate. Sharp gravel wears the barbels off a corydoras over a month or two, and a cory that has lost its barbels cannot feed properly, so smooth sand is not optional. The third is the otocinclus starvation trap already named, and the fourth is expecting any of them to be a cleanup crew: they still need sinking food of their own, and the tank still needs its weekly water change. A bottom fish is a resident with a job, not a filter you feed once.

Frequently asked questions

What is the best bottom-dweller for a 10-gallon tank?

Pygmy corydoras. At 1 inch and in a group of eight, they fit a planted 10-gallon where a bronze corydoras (which wants a 20-gallon floor) would be cramped. They are peaceful, active, safe with shrimp, and want the same 72 to 79 F water as most nano schoolers. A small otocinclus group works too, but only in a tank over three months old.

Do bottom-feeder fish clean the tank?

Only partly. They eat leftover food and graze the substrate and algae, which keeps the lowest level turned over, but they do not remove dissolved waste, so they do not replace a filter or a water change. Feeding a bottom fish sinking food is still necessary; they do not live on your leftovers alone.

Why is my corydoras hiding or losing its barbels?

Hiding usually means the group is too small: corydoras want six or more or they stay tucked away. Worn or missing barbels almost always mean sharp gravel, which grinds them down, so switch to smooth sand. Both are design problems you prevent, not something to diagnose after the fact.

Can bottom-dwellers live with shrimp?

Adult shrimp, yes. Pygmy corydoras, otocinclus, and kuhli loaches are all safe with an adult cherry shrimp colony, and none of them hunts a grown shrimp. Newborn shrimp are small enough that any bottom forager may take a few, so heavy moss cover is what keeps a colony reproducing alongside them.

How many bottom-dwellers can I keep?

Count them into your total bioload rather than treating them as free cleanup. A planted 20-gallon holds one bottom group (six corydoras or five kuhli) alongside a mid-water school and a centerpiece comfortably. Do not stack three different bottom species in a small tank; pick one and give it a proper group.

Give a bottom fish sand, a group, and cover, and it works the floor of a planted community for years. Run your stocking through the build planner for a balanced, level-by-level list, check any species against its record in the livestock database, and read aquarium fish and plant compatibility for how the bottom crew fits the plants above it. For a centerpiece to sit over the top, the best nano centerpiece fish pairs well, and if you are weighing a land enclosure instead of a tank, the crested gecko vs dart frog comparison covers the vivarium route.