Types of Aquarium Algae: 12 Kinds and How to Get Rid of Them

How to recognise it

A dull tan or rust-coloured dust that settles evenly over glass, sand and older leaves within the first weeks of a new setup. It wipes off with a finger and clouds the water as it lifts, leaving clean glass behind with almost no pressure — that easy removal is the single best identifier. It appears first on the shaded side of the tank and on the substrate, not in the brightest spot.

What causes it

Silicates leaching from new sand, new substrate and tap water, combined with an immature filter that has not yet stabilised ammonia and nitrite. It is a new-tank phenomenon, not a lighting problem — dimming the light does very little.

What eats it

• Otocinclus — strips diatoms off glass and leaves faster than anything else, but needs a tank mature enough to feed it once the diatoms are gone.
• Twig catfish — grazes the same film from leaves and wood without damaging plants, though it needs stable water and supplemental veg.

How to remove it

Manual:

Wipe the glass with a melamine sponge and siphon the top layer of substrate during water changes — it lifts immediately.

Husbandry:

Finish cycling the tank and keep water changes weekly. Silicate depletes on its own as the substrate ages; adding fast-growing stem plants speeds it up by consuming the remaining nutrients.

Chemical:

None needed, and none worth using. Silicate-removing resin exists for reef tanks but is pointless expense in freshwater, where the outbreak ends by itself.

How to recognise it

Hard, flat green dots roughly 1–3 mm across, evenly spaced on the brightest pane of glass and on the oldest leaves of slow growers such as anubias. It does not smear when you wipe it — a cloth passes straight over it and a razor or hard scraper is needed. If it resists a melamine sponge, it is green spot.

What causes it

Low phosphate in a tank with strong light. Counterintuitively this is a deficiency problem, not an excess one: starved plants stop competing and Coleochaete colonises the brightest hard surfaces.

What eats it

• Nerite snail — the only reliable grazer of hardened green spot — one per 40 L keeps glass clear, though it leaves cosmetic white eggs behind.

How to remove it

Manual:

A plastic or steel blade on glass; on anubias, trim the worst affected old leaves rather than scrubbing them.

Husbandry:

Raise phosphate rather than cutting it — dosing to roughly 1 ppm PO4 stops new spots forming within a fortnight. Reduce the photoperiod to 6–7 hours if the tank sits over 8.

Chemical:

Nothing spot-treats it effectively. Algaecides bleach it without removing the calcified base, so it stays visible on the glass.

How to recognise it

A fine green haze that veils the entire pane rather than forming discrete dots, and returns within two or three days of every wipe. Sheets of it slough off on their own and drift through the water column. The give-away is the cycle: clean glass, green glass in 72 hours, repeat.

What causes it

A spore stage that reinfects the glass the moment you wipe it. Wiping is the trigger — every clean releases the next generation before it has matured and settled.

What eats it

• Bristlenose pleco — grazes the film continuously and is the only pleco that belongs in a normal community tank.
• Rubber lip pleco — keeps eating film algae into adulthood, unlike common plecos, and suits cooler tanks.

How to remove it

Manual:

Do the opposite of instinct: leave the glass alone for three to four weeks. The mature layer detaches in sheets on its own, and can then be siphoned out in a single session.

Husbandry:

Keep water changes and feeding normal during the wait. Cutting light does not shorten the cycle.

Chemical:

Not appropriate — the outbreak is self-limiting and dosing peroxide simply restarts the cycle.

How to recognise it

The water itself turns green and you lose sight of the back glass, while the glass, plants and hardscape stay clean. Free-floating single cells, not attached growth — nothing to wipe, nothing to scrape.

What causes it

An ammonia spike combined with strong light: a disturbed substrate, an overhaul of the filter, a dead fish behind the hardscape, or direct sunlight on the tank. Nitrate alone does not do this; the ammonia pulse does.

What eats it

No aquarium fish or shrimp clears green water — the cells are too small to graze. Daphnia will consume it in a bucket, but your filter and lighting do the real work.

How to remove it

Manual:

Water changes barely help; you remove green water and the remaining cells double back within a day. A UV steriliser clears it reliably in 24–72 hours and is the single most effective tool.

Husbandry:

Find and remove the ammonia source, then run a three-day total blackout with the tank wrapped in a blanket and the lights off. Move the tank out of direct sunlight.

Chemical:

Flocculants clump the cells so the filter can catch them, but they clog filter floss quickly and do nothing about the cause.

How to recognise it

Long single strands, several centimetres to a hand-span, that wrap around stems and equipment and can be wound onto a toothbrush like candy floss. It feels slimy rather than coarse — Spirogyra in particular slips through the fingers, which separates it from the rough branching types below.

What causes it

Excess nitrate with a nutrient the plants are short of, most often in tanks that have just been dosed heavily or where a CO2 system has been added without matching light and fertiliser.

What eats it

• Cherry shrimp — a colony picks at soft threads constantly and prevents regrowth, but will not clear an established mat on its own.

How to remove it

Manual:

Twirl it out with a toothbrush weekly — physical removal is far more effective here than on any other type.

Husbandry:

Balance the dosing rather than cutting it: test nitrate, keep it near 10–20 ppm, and make sure the plants have the light and CO2 to use what you add. Increase flow past the affected stems.

Chemical:

Spot-dosing liquid carbon with the filter off works on Spirogyra, but it damages vallisneria and some mosses at treatment strength.

How to recognise it

A short, soft green fuzz, 5–20 mm, growing directly out of leaf edges and giving the plant a furred outline. Unlike thread algae it will not wind onto a brush — it comes away with the leaf tissue, which is why it is so often confused with a struggling plant rather than an algal outbreak.

What causes it

Unstable or insufficient CO2 in a lit planted tank. Plants that cannot photosynthesise at the rate the light demands leak nutrients from the leaf surface, and Oedogonium settles there.

What eats it

• Amano shrimp — genuinely clears it — six amanos will strip a hair algae outbreak in a 100 L tank in about a week, the most reliable biological fix on this page.

How to remove it

Manual:

Trim the worst affected leaves entirely; picking fuzz off a leaf tears it.

Husbandry:

Stabilise CO2 before anything else — same injection rate, same start time daily, and check the drop checker is green two hours before lights on. Drop the photoperiod to 6 hours while you fix it.

Chemical:

Liquid carbon spot-dosing kills it in a couple of days, but treats the symptom; it returns within a fortnight if CO2 stays unstable.

How to recognise it

Coarse, wiry, branching filaments that form a tangled mat and smell faintly musty when pulled out of the water. It is noticeably tougher than thread algae — you feel it resist between your fingers rather than slide. Once it works into moss or a carpet it is effectively impossible to separate.

What causes it

Usually introduced, not spontaneous. It arrives on plants, moss or a Marimo ball and establishes in dead spots where flow is poor and detritus collects.

What eats it

Nothing eats Cladophora. Shrimp will pick at detritus caught in it and give the impression of progress, but the filaments themselves are ignored.

How to remove it

Manual:

Remove it by hand along with the substrate or hardscape it is anchored to. Badly infested moss and carpets should be thrown out rather than treated.

Husbandry:

Increase flow through the dead spot and siphon detritus out of it, or it will re-establish from fragments.

Chemical:

Excel or hydrogen peroxide spot-dosing with the filter off works, but needs repeating for several weeks and is hard on shrimp and mosses.

How to recognise it

Stiff grey-green tufts that branch like antlers from leaf tips and equipment, 10–20 mm long, firmly anchored and unwilling to be pulled off. The diagnostic test: a tuft dropped into household bleach diluted 1:20 turns red within a minute, because Compsopogon is a red alga.

What causes it

Organic waste build-up combined with poor water circulation — an overdue filter clean, a substrate never siphoned, or a tank stocked past what its maintenance routine supports.

What eats it

• Chinese algae eater — sold for exactly this job and does not do it — it ignores staghorn as an adult and turns on slow, flat-bodied tankmates instead. Skip it.

How to remove it

Manual:

Cut off affected leaves and scrub hardscape outside the tank; it will not brush off in place.

Husbandry:

Clean the filter, siphon the substrate properly, and cut feeding. Once organics drop, new tufts stop appearing quickly.

Chemical:

A three-minute dip in 1:20 bleach for hardscape and hardy plants kills it outright; rinse and dechlorinate thoroughly before returning anything.

How to recognise it

Dense black tufts, 2–15 mm, that grow exactly where flow is fastest — the outlet nozzle, the edges of leaves that face the current, the upstream face of driftwood. It grips so hard that pulling it takes the leaf with it. Bleach turns it red, like staghorn, because it is also a red alga.

What causes it

Fluctuating CO2 above all else — a cylinder running out, a solenoid on a drifting timer, or heavy surface agitation dumping CO2 at night. Secondary triggers are old, unmaintained filter media and high organic load.

What eats it

• Siamese algae eater — the only species with any real record on BBA, and only when genuinely hungry and correctly identified — most fish sold under this name are flying fox or worse. Treat it as a bonus, never as the plan.

Be plain about this: no fish, shrimp or snail reliably eats black beard algae. If someone sells you a clean-up crew as the solution, they are selling you the wrong thing.

How to remove it

Manual:

Remove affected leaves and take hardscape out for treatment. Scrubbing in place spreads fragments.

Husbandry:

Fix CO2 stability first — steady injection, same schedule, no overnight swing. Then clean the filter and reduce the organic load. Nothing else works long term.

Chemical:

Spot-dose 3% hydrogen peroxide or liquid carbon directly onto tufts with the filter off for 10 minutes. It turns pink, then white, then dies over 3–5 days. Effective but purely cosmetic if CO2 stays unstable.

How to recognise it

Flat, hard, dull red patches crusted onto stone and glass, with no texture above the surface — closer to a stain than a growth. It cannot be wiped, brushed or scraped off cleanly and it does not spread quickly. Rare in aquaria and usually found in tanks running for a year or more.

What causes it

Long-established surfaces with steady low light. It is a slow coloniser rather than a nutrient-driven bloom, and it is not a sign of anything wrong with the tank.

What eats it

Nothing grazes it. The crust is calcified into the surface and no aquarium animal can get purchase on it.

How to remove it

Manual:

A razor on glass; on rock, physical abrasion or replacing the stone are the only real options.

Husbandry:

No husbandry change removes it, because no common husbandry fault caused it.

Chemical:

A bleach dip for removable hardscape. In-tank dosing does not lift the crust.

How to recognise it

A slick sheet that peels off in one piece like wet tissue rather than breaking up, and a strong, unmistakable earthy or swampy smell on your hands afterwards. It creeps across the sand at the front glass first. If it comes away as a single film and smells, it is cyanobacteria — nothing else does both.

What causes it

Stagnant water with organic waste, typically low nitrate and low flow together: an under-siphoned substrate, a filter pointed away from the front corners, or a heavily fed tank with sparse plants.

What eats it

Nothing eats cyanobacteria, and nothing should — some strains produce toxins. This is the clearest case on the page where a clean-up crew is the wrong answer.

How to remove it

Manual:

Siphon the sheets out whole during a large water change; they lift cleanly.

Husbandry:

Redirect flow into the dead spot, siphon the substrate thoroughly, cut feeding, and raise nitrate to 10–20 ppm — starving nitrate makes cyanobacteria worse, not better. A three-day blackout after siphoning kills most of it.

Chemical:

Erythromycin at 200 mg per 40 L clears it in 3–5 days and is the reliable option, but it also hits the filter bacteria — test ammonia daily for a week afterwards.

How to recognise it

A slippery white or greyish jelly, sometimes stringy like cotton wool, appearing on freshly submerged driftwood within the first week or two. It wafts in the current, comes off with a gentle brush, and only ever sits on the wood — never on glass or leaves.

What causes it

Sugars and soft tissue leaching out of new wood feed a bloom of bacteria and fungi. It is a stage of the wood curing, not a water quality failure.

What eats it

• Clown pleco — lives on driftwood and rasps the film away as part of its normal grazing — one of the few problems on this page that genuinely solves itself with livestock.

How to remove it

Manual:

Brush it off and siphon it out at a water change, or simply leave it alone.

Husbandry:

Nothing needed. Boiling or soaking the wood before it goes in shortens the phase.

Chemical:

Never appropriate — dosing anything here treats a harmless, temporary bloom.