AquariumStocking
    Buying Guide
    10 min read

    Aquarium Algae Eaters: Algae Eating Fish for Every Tank Size

    Two questions decide which algae eater belongs in your tank: what the algae is, and how much water you have. Get either wrong and you end up with a fish that ignores the algae, outgrows the tank, or starves once the glass is clean. This guide sorts eleven species that genuinely work by algae type and by tank size, and names the one sold in every shop that you should walk past.

    Reviewed by the AquariumStocking team · Updated

    Collage of aquarium algae eaters: bristlenose pleco, otocinclus, amano shrimp and nerite snail

    Match the eater to the algae

    Find the algae you have on the left, and the species that measurably eat it on the right. Where the honest answer is "nothing", the row says so — those types are fixed by light, nutrients and flow, not by livestock.

    Algae typeWhat actually eats itReality check
    Brown diatomsOtocinclus, nerite snail, ramshorn snailThe easiest type to clear. Usually fades on its own as a new tank matures.
    Green dust algaeNerite snail, otocinclus, ramshorn snailGrazers keep glass clear, but the film returns until the photoperiod comes down.
    Green spot algaeNerite snail (the only reliable one)Hard-shelled and stuck fast. Most fish cannot rasp it off; a blade finishes the job.
    Green hair and fuzz algaeAmano shrimp, siamese algae eater, bristlenose plecoSix amanos will strip a small outbreak in a week. Manual removal first speeds it up.
    Thread algaeAmano shrimp, siamese algae eaterTwirl it out on a toothbrush before adding livestock — long strands foul filters.
    Cladophora (branching)Nothing reliablyTough, wiry and unpalatable. Remove by hand or spot-dose; livestock will not touch it.
    Staghorn algaeSiamese algae eater, occasionallyOnly when genuinely hungry. Flow and CO2 stability matter far more than the fish.
    Black beard algaeSiamese algae eater, occasionallyBuying an SAE as a cure is the classic mistake. Fix CO2, flow and phosphate instead.
    Red spot algaeNothing reliablyScrape it. It sits in the same family as black beard and resists grazing the same way.
    Green waterNothingFree-floating cells. A UV steriliser or a blackout clears it; grazers cannot reach it.
    Cyanobacteria (blue-green)Nothing — and it is not algaeA bacterium. Toxic to most grazers. Blackout, siphon and improve flow.
    White driftwood biofilmAmano shrimp, cherry shrimp, snailsHarmless fungal bloom on new wood. The shrimp treat it as a buffet and it passes.

    Not sure which of these you are looking at? Every type above is photographed and described in our aquarium algae identification guide

    How to choose

    Name the algae before you buy anything

    A soft brown dust on the glass of a two-month-old tank, a hard green dot you need a blade to shift, and a black tuft on a leaf edge are three different organisms with three different answers. Otocinclus clear the first, nerites handle the second, and almost nothing touches the third. If you cannot name what you are looking at, work through the identification guide first and come back with an answer.

    Buy for the tank you own, not the tank you want

    Every species below is placed in a tank-size band using the minimum footprint from our species database, not the sticker on the shop tank. A 20 gallon has room for otocinclus, snails and shrimp. It has no room for a common pleco that reaches 45 cm, or a chinese algae eater that reaches 25 cm and turns on its tankmates. Those two purchases account for most of the rehoming requests in beginner forums.

    Plan to feed them

    A cleanup crew that works puts itself out of a job within weeks, and then it needs dinner like everything else. Bristlenose, rubber lip plecos, twig catfish and amano shrimp all take sinking wafers, blanched courgette and repashy. Drop food in after lights-out and pull anything uneaten the next morning so you are not feeding the algae you just removed.

    Count the group, then count the bioload

    Otocinclus and cherry shrimp are group animals and behave badly alone or in pairs; snails and most plecos are singles. Whatever the number, the crew still breathes, eats and produces waste, so it goes into the stocking maths alongside your fish rather than sitting outside it. A shoal of six otos in a 20 gallon is real stock, not free labour.

    Nano tanks — under 10 gallons

    No fish belongs on cleanup duty at this volume. Invertebrates do the whole job: they graze constantly, add almost nothing to the bioload, and fit a tank measured in inches rather than feet. One nerite plus a small shrimp colony keeps a nano spotless.

    Two nerite snails on a piece of driftwood in an aquarium

    Nerite Snail

    Neritina sp.

    The single most effective grazer per gallon in the hobby, and the only common animal that reliably removes green spot algae. It works over glass, hardscape and leaf surfaces without damaging plants, and it cannot breed in freshwater, so the population never runs away from you.

    Eats
    Green spot, green dust, brown diatoms, film on glass and hardscape
    Won't touch
    Hair algae, thread algae, black beard, cyanobacteria
    Group
    Kept singly — roughly one per 40 L / 10 gallons
    The catch
    Lays hard white eggs on every surface. They never hatch, but they do not brush off either.
    Min tank 5 gallons+
    72-79°F
    pH 7–8.5
    2.5 cm (1")
    Peaceful
    Beginner
    Full Nerite Snail profile
    Amano shrimp eating a piece of algae wafer at the bottom of an aquarium

    Amano Shrimp

    Caridina multidentata

    The one to buy when hair or thread algae has taken hold. Amanos are big enough to survive alongside most community fish and busy enough to work through an outbreak that snails would take months over. They stay productive at tropical temperatures where many shrimp slow down.

    Eats
    Hair algae, thread algae, soft film, leftover food, new driftwood biofilm
    Won't touch
    Green spot algae, black beard, cyanobacteria
    Group
    Six or more — singles hide and you never see them working
    The catch
    Will not breed in freshwater, so the colony never replaces itself, and they raid shrimp fry.
    Min tank 5 gallons+
    68-79°F
    pH 6.5–7.5
    5 cm (2")
    Peaceful
    Beginner
    Full Amano Shrimp profile
    Close up of cherry shrimp at the bottom of an aquarium

    Cherry Shrimp

    Neocaridina davidi

    Less of a heavy-duty algae crew than amanos and more of a permanent maintenance colony. They pick constantly at soft film and detritus, breed readily in a stable nano, and become self-sustaining stock rather than a purchase you repeat.

    Eats
    Soft green film, biofilm, detritus, decaying leaves
    Won't touch
    Established hair algae, green spot, anything hard-shelled
    Group
    Ten or more to start a stable breeding colony
    The catch
    Eaten by almost anything larger, and copper in medication or tap water kills the whole colony.
    Min tank 5 gallons+
    64-82°F
    pH 6.5–8
    3 cm (1.2")
    Peaceful
    Beginner
    Full Cherry Shrimp profile
    Red ramshorn snail slowly moving on aquarium substrate

    Ramshorn Snail

    Planorbella duryi

    Usually arrives uninvited on plants, which is why keepers underrate it. In a nano it is a genuinely useful diatom and film grazer that also clears uneaten food from the substrate before it rots.

    Eats
    Brown diatoms, soft film, decaying plant matter, leftover food
    Won't touch
    Green spot, hair algae, healthy plant tissue
    Group
    Self-regulating — start with two or three
    The catch
    Breeds to match the food supply. A population explosion is an overfeeding signal, not a snail problem.
    Min tank 2 gallons+
    64-82°F
    pH 7–8
    2 cm (0.8")
    Peaceful
    Beginner
    Full Ramshorn Snail profile

    Small tanks — 10 to 29 gallons

    This is where the damage usually happens. A 20 gallon is the tank a common pleco or a chinese algae eater is most often sold for, and both are wrong: the pleco reaches 45 cm and needs over 100 gallons, the chinese algae eater reaches 25 cm and starts attacking tankmates long before that. At this size the right answers are a shoal of otocinclus, a clown pleco on driftwood, or a snail.

    Otocinclus resting on a piece of lava rock in an aquarium

    Otocinclus

    Otocinclus vittatus

    The best small algae-eating fish there is, and the one most often killed by being bought too early. Otos are specialists in the soft brown and green film that coats a maturing planted tank, working leaves that snails cannot cling to. Add them to a tank that is at least two months old with visible biofilm already present.

    Eats
    Brown diatoms, soft green film on leaves and glass
    Won't touch
    Hair algae, green spot, black beard, anything tough
    Group
    Six minimum — smaller groups stop feeding and waste away
    The catch
    Wild-caught, arrive stressed, and starve in a clean tank. Supplement with courgette once the film is gone.
    Min tank 15 gallons+
    72-79°F
    pH 6–7.5
    4 cm (1.6")
    Peaceful
    Intermediate
    Full Otocinclus profile
    Clown pleco laying at the bottom of an aquarium substrate

    Clown Pleco

    Panaqolus maccus

    The pleco that actually fits a 20 gallon, provided the tank has driftwood — it rasps wood as a dietary requirement, not a preference. Buy it as a small, characterful bottom dweller that keeps biofilm down, and you will be happy; buy it to clear green algae and you will not.

    Eats
    Driftwood biofilm, soft algae on wood, sinking wafers
    Won't touch
    Green spot on glass, hair algae, thread algae
    Group
    One per tank — males hold territory under wood
    The catch
    No driftwood means a slow decline. It is a wood eater first and an algae eater second.
    Min tank 20 gallons+
    75-86°F
    pH 6–7.5
    9 cm (3.5")
    Peaceful
    Beginner
    Full Clown Pleco profile
    A yellow mystery snail walking on a marimo moss ball in an aquarium

    Mystery Snail

    Pomacea bridgesii

    A large, visible snail that earns its place as a scavenger rather than a glass cleaner. It hoovers uneaten food, dying leaves and soft film, which keeps the nutrients that feed algae from accumulating in the first place.

    Eats
    Leftover food, soft film, dying plant matter, blanched vegetables
    Won't touch
    Green spot, hair algae, black beard
    Group
    One or two — they are a noticeable bioload for their size
    The catch
    Needs calcium-rich, alkaline water or the shell pits, and will nip soft new plant growth if underfed.
    Min tank 5 gallons+
    68-82°F
    pH 7–8
    6 cm (2.4")
    Peaceful
    Beginner
    Full Mystery Snail profile

    Medium tanks — 30 to 55 gallons

    The first band with room for a proper algae-eating fish. A bristlenose is the default recommendation here and deserves it, but rubber lip plecos and twig catfish suit specific setups better — cooler water in one case, heavily planted and calm in the other.

    Bristlenose pleco laying at the bottom of an aquarium

    Bristlenose Pleco

    Ancistrus sp.

    The default answer for a community tank of this size and the only plecostomus most keepers should ever buy. It stays under 12 cm, keeps grazing green algae into adulthood instead of losing interest, tolerates ordinary community parameters, and breeds in a cave without any intervention.

    Eats
    Green spot algae, green dust, diatoms, soft hair algae, wood biofilm
    Won't touch
    Black beard algae, cladophora, cyanobacteria
    Group
    One per 100 L / 25 gallons — two males will fight over caves
    The catch
    A real bioload. It needs wood to rasp and wafers or vegetables most days once the glass is clean.
    Min tank 30 gallons+
    73-81°F
    pH 6–7.5
    12 cm (4.7")
    Peaceful
    Beginner
    Full Bristlenose Pleco profile
    Rubber lip pleco sucking on a rock in an aquarium

    Rubber Lip Pleco

    Chaetostoma formosae

    The one to pick when the tank runs cool. It keeps grazing well into adulthood, handles 18–24 °C comfortably, and suits hillstream and subtropical community setups where a bristlenose would be sluggish. Underrated, and rarely stocked, which is the only reason it is not the standard recommendation.

    Eats
    Green film, diatoms, soft green algae on glass and hardscape
    Won't touch
    Black beard algae, thread algae, cladophora
    Group
    One per tank
    The catch
    Wants oxygenated water with real current — it does poorly in a still, warm tank.
    Min tank 30 gallons+
    70-79°F
    pH 6.5–7.5
    12 cm (4.7")
    Peaceful
    Beginner
    Full Rubber Lip Pleco profile
    Twig catfish laying on a bare bottom fish tank

    Twig Catfish

    Farlowella acus

    A stick-thin oddity that grazes film algae off leaves, wood and glass without bruising a single plant. Choose it for a mature, quietly stocked planted tank where its slow feeding will not be outcompeted at every meal.

    Eats
    Soft green film on leaves and wood, biofilm, blanched vegetables
    Won't touch
    Green spot algae, hair algae, black beard
    Group
    One, or a pair in a tank of 150 L / 40 gallons and up
    The catch
    Sensitive to nitrate swings and easily starved by fast, greedy tankmates. Not a beginner fish.
    Min tank 30 gallons+
    75-82°F
    pH 6–7.5
    16 cm (6.3")
    Peaceful
    Advanced
    Full Twig Catfish profile

    Large tanks — 55 gallons and up

    Volume buys you the only fish with a real record against hair, thread and occasionally black beard algae. It also buys the space that fish needs as it matures and gets pushier, which smaller tanks cannot give it.

    Siamese Algae Eater foraging for food at the bottom of an aquarium

    Siamese Algae Eater

    Crossocheilus oblongus

    The only fish with a genuine, repeatable record against hair and thread algae, and the only one that sometimes eats black beard algae. Reaching 15 cm and becoming steadily more assertive, it needs the room a 55 gallon or larger gives it. Check the black stripe runs all the way into the tail — flying fox and chinese algae eater are sold under the same name.

    Eats
    Hair algae, thread algae, staghorn, sometimes black beard when hungry
    Won't touch
    Green spot algae, cyanobacteria, cladophora
    Group
    One, or five and up — a group of two or three bullies the weakest
    The catch
    Once it discovers flake food it largely stops working, and it harasses slow long-finned fish as it ages.
    Min tank 30 gallons+
    75-79°F
    pH 6.5–7.5
    15 cm (5.9")
    Peaceful
    Beginner
    Full Siamese Algae Eater profile

    Sold as an algae eater — buy something else

    This one appears in the same shop tank as the siamese algae eater, at half the price, under a near-identical label. It is not an equivalent.

    Yellow chinese algae eater eating algae while laying on aquarium driftwood

    Chinese Algae Eater

    Gyrinocheilus aymonieri

    Not recommended. Grows to 25 cm, stops eating algae as an adult, and rasps the slime coat of flat-bodied tankmates. A bristlenose pleco or a true siamese algae eater does the job without the damage.

    Sold cheaply beside the siamese algae eater and mistaken for it constantly. It grazes for a few months as a juvenile, then reaches 25 cm, abandons algae almost entirely, and turns aggressive — including latching onto the flanks of flat-bodied fish such as goldfish, angelfish and discus to rasp their slime coat, which causes wounds and infection. Buy a bristlenose pleco or a true siamese algae eater instead.

    Eats
    Soft algae as a juvenile only
    Won't touch
    Almost any algae once mature — it switches to prepared food
    Group
    One at most, and not in a community tank
    The catch
    Reaches 25 cm, needs 55 gallons on its own merits, and injures slow tankmates.
    Min tank 55 gallons+
    75-82°F
    pH 6–8
    25 cm (9.8")
    Aggressive
    Beginner
    Full Chinese Algae Eater profile

    Algae eaters won't fix an algae problem

    Algae grows where light and nutrients exceed what the plants and bacteria in the tank can use. A cleanup crew removes the visible result; it does nothing about the cause. Add six otos and a bristlenose to a tank running a ten-hour photoperiod with heavy feeding and you have not solved anything — you have added a bioload that raises nitrate and phosphate, which is the fuel the algae was growing on in the first place.

    Work in this order. Identify what you are actually dealing with, because a cyanobacteria mat and a diatom film need opposite responses. Cut the photoperiod to six or seven hours on a timer. Feed less, and siphon what settles. Add fast-growing stem plants and floaters so something is competing for the nutrients. Then, once the tank is stable, bring in a crew sized to the volume rather than sized to your frustration.

    Sized to the volume is the part people skip. Run the crew through the stocking calculator with the rest of your fish before you buy — six otocinclus and a bristlenose are real stock in a 30 gallon, not a free service.

    Compare at a glance

    Sort by any column — tap a header to reorder.

    Ramshorn Snail2 gallons64-82°F7–82 cm (0.8")BeginnerPeaceful
    Nerite Snail5 gallons72-79°F7–8.52.5 cm (1")BeginnerPeaceful
    Amano Shrimp5 gallons68-79°F6.5–7.55 cm (2")BeginnerPeaceful
    Cherry Shrimp5 gallons64-82°F6.5–83 cm (1.2")BeginnerPeaceful
    Mystery Snail5 gallons68-82°F7–86 cm (2.4")BeginnerPeaceful
    Otocinclus15 gallons72-79°F6–7.54 cm (1.6")IntermediatePeaceful
    Clown Pleco20 gallons75-86°F6–7.59 cm (3.5")BeginnerPeaceful
    Bristlenose Pleco30 gallons73-81°F6–7.512 cm (4.7")BeginnerPeaceful
    Rubber Lip Pleco30 gallons70-79°F6.5–7.512 cm (4.7")BeginnerPeaceful
    Twig Catfish30 gallons75-82°F6–7.516 cm (6.3")AdvancedPeaceful
    Siamese Algae Eater30 gallons75-79°F6.5–7.515 cm (5.9")BeginnerPeaceful
    Chinese Algae Eater55 gallons75-82°F6–825 cm (9.8")BeginnerAggressive

    Not sure how many will fit?

    Drop your tank size and shortlist into the stocking calculator to see real bioload, swim-level balance, and compatibility flags.

    Frequently asked questions

    What is the best algae eater for a small aquarium?

    Under 10 gallons, use invertebrates only: a nerite snail for glass and hardscape, plus amano or cherry shrimp for film and detritus. From 10 to 29 gallons a shoal of six otocinclus is the best algae eating fish available. No pleco belongs below 30 gallons, and the common pleco needs over 100.

    Which algae eater eats hair algae?

    Amano shrimp are the most reliable, and a group of six will strip a small outbreak within a week. Siamese algae eaters work on hair and thread algae in tanks of 55 gallons or more. Pull out the long strands by hand first — livestock clears what is left far faster than it clears a full mat.

    Do any aquarium algae eaters eat black beard algae?

    Only the siamese algae eater, and only when it is genuinely hungry and has not learned to prefer flake food. Treat that as a bonus rather than a plan. Black beard algae responds to stable CO2, better flow and lower phosphate, so fix those before buying a fish for it.

    How many algae eaters does my tank need?

    Roughly one nerite per 10 gallons, one amano shrimp per 5 gallons during an outbreak, six or more otocinclus in tanks from 16 gallons, and one bristlenose pleco per 25 gallons. More is not better: an oversized crew strips the tank and then starves.

    Are chinese algae eaters good algae eaters?

    No. They graze as juveniles, then reach 25 cm, largely stop eating algae, and become aggressive — attaching to the flanks of goldfish, angelfish and discus to rasp their slime coat. They are frequently mis-sold as siamese algae eaters. Choose a bristlenose pleco or a true siamese algae eater instead.

    Can I put a pleco in a 20 gallon tank?

    Only a clown pleco, and only with driftwood in the tank. A bristlenose needs 30 gallons and a common pleco reaches 45 cm and needs over 100. The common pleco sold as a two-inch juvenile for a 20 gallon community tank is the single most common stocking mistake in the hobby.

    Why does my algae eater keep dying?

    Three usual causes: the tank was too new and had no biofilm to graze, nobody supplemented food once the algae ran out, or copper from medication or tap water poisoned the invertebrates. Otocinclus and shrimp are sensitive to all three, so add them to mature tanks and feed them deliberately.

    Will algae eaters clear green water?

    No. Green water is free-floating single-celled algae suspended in the water column, and grazers can only work surfaces. A three-day blackout, a UV steriliser or a large water change with reduced lighting clears it. No livestock purchase will.

    Do algae eaters eat plants?

    Healthy plants, generally no. Underfed mystery snails and hungry bristlenose plecos will rasp holes in soft new growth such as amazon sword leaves, which is a feeding signal rather than a species trait. Amano shrimp and otocinclus leave plants alone entirely.