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Black beard algae: how to identify it, kill it and stop it coming back

Not urgent

Black beard algae (often called BBA) is a tough red algae that grows in dark, bristly tufts on plant edges, wood, rocks and filter pipes. It won't hurt your fish, but it smothers slow plants and is hard to remove, so the real fix is changing what lets it grow, usually unsteady CO2 or poor water flow.

You can kill existing tufts with careful spot treatment or by scrubbing and boiling decor. Then steady the tank so it doesn't grow back.

How to identify it

  • Short, dense tufts or "beards", usually 2 to 20 mm (up to about 3/4 inch) long.
  • Black, dark grey, dark green or reddish. Despite the name, it's a red algae, in a group called Audouinella.
  • Tough and rough, not slimy. It clings hard and doesn't wipe off. Rub a tuft between your fingers: it feels like soft bristles.
  • Where it grows: edges of slow-growing leaves (anubias, java fern), driftwood, rocks, filter intakes and outlets, heater cords, and the rim of the tank.

Not BBA: green hair algae is long, soft and bright green. Brown diatoms wipe off easily (see brown algae). Blue-green slime that peels off in sheets and smells is cyanobacteria.

When it's a problem

  • Normal: a few small tufts on old leaves or the filter. Many tanks have a little.
  • Early problem: new tufts appearing every week, spreading along leaf edges and wood.
  • Serious: slow plants covered and dying, decor coated, tufts spreading even after you trim.
  • Emergency: BBA is never an emergency for fish. Only rush if you've dosed a treatment and fish are gasping (do a big water change at once).

What to do right now

  1. Don't panic or reach for strong chemicals. Fish are safe.
  2. Trim the worst leaves at the base with scissors. Badly covered leaves won't recover.
  3. Take out decor you can remove (rocks, ornaments, wood without plants attached) and scrub it with a stiff brush outside the tank.
  4. Check your CO2 if you inject it. Is the bottle nearly empty? Is the diffuser clogged? Does the drop checker change colour during the day?
  5. Check flow. Clean the filter in tank water and remove anything blocking circulation.
  6. Test nitrate and phosphate, and do a water change if they're high.

What to do next

Spot treatment with liquid carbon (glutaraldehyde). "Liquid carbon" products contain glutaraldehyde, which kills BBA on contact.

  1. Turn off the filter and pump so the water is still.
  2. Use a syringe or dropper to squirt the product directly onto tufts, a little at a time. Stay within the product's daily maximum for your tank's volume.
  3. Wait 5 to 15 minutes, then turn the filter back on.
  4. Over several days, treated BBA turns pinkish-red or white, then grey. Fish, snails or shrimp often eat it once it's dead. Brush away what's left.

Cautions: vallisneria, mosses, some crypts and other sensitive plants can melt from glutaraldehyde. It's a disinfectant, so wear gloves, and avoid overdosing in tanks with shrimp. Don't use it alongside other medicines without checking.

Spot treatment with hydrogen peroxide (3%). Ordinary pharmacy hydrogen peroxide also kills BBA. Apply small amounts with a syringe directly onto tufts with the filter off, and the algae will fizz. Sources give very different whole-tank doses, so stick to small spot doses. Too much harms filter bacteria, mosses and shrimp, and can burn fish gills. If fish start gasping, change water at once.

Treat removed items outside the tank. This is the safest option for rocks, ornaments and hardy plants.

  • Boil rocks and ornaments that can take the heat for 10 to 15 minutes, then let them cool. Don't boil glued decor or anything plastic that could warp.
  • Soak in a stronger mix of hydrogen peroxide or liquid carbon in a bucket, then rinse well.
  • Bleach dip (1 part plain unscented bleach to about 20 parts water) for hard decor and very hardy plants like anubias, only for a minute or two for plants. Rinse thoroughly and soak in water with a double dose of dechlorinator before putting back. This is the riskiest method.

Weeks 2 to 8: fix the cause. Treatment alone almost never works. BBA grows back unless you change the conditions it likes:

  • Make CO2 steady. Start injected CO2 one to two hours before the lights come on, so the level is already stable. Don't let the bottle run dry. In tanks without injected CO2, avoid using liquid carbon on some days and not others.
  • Improve flow so there are no dead spots, and water moves gently across all plants.
  • Replace old bulbs or tubes on their recommended schedule, and keep light to 6 to 8 hours a day.
  • Do regular water changes and keep the substrate clean, since BBA likes dirty, nutrient-heavy tanks.
  • Add fast-growing plants to use up nutrients.

Algae eaters. Very few animals eat BBA. The true Siamese algae eater (Crossocheilus) is the most reliable, especially when it's not overfed. It grows to about 15 cm (6 inches), lives in groups and needs a tank of about 110 litres (30 US gallons) or more. Make sure you're not sold the similar-looking Chinese algae eater, which becomes aggressive. Florida flagfish and Amano shrimp eat young growth, and many animals happily eat BBA once a treatment has killed it.

Products that help

  • Liquid carbon (glutaraldehyde): spot-treats tufts. Use with care around sensitive plants and shrimp.
  • 3% hydrogen peroxide: spot treatment or dips for removed decor.
  • Syringe or dropper: puts treatment exactly where it's needed.
  • Stiff brush and algae scraper: removes dead and live algae from rocks and glass.
  • CO2 drop checker and a solenoid timer: show and steady CO2 levels in injected tanks.
  • Light timer: keeps the light period steady.
  • Keep on hand: sharp plant scissors and a test kit for nitrate and phosphate.

How to prevent it

  • Keep CO2 steady from lights-on to lights-off.
  • Keep flow good everywhere, and clean the filter regularly.
  • Don't overfeed. See the overfeeding guide.
  • Inspect and dip new plants and second-hand decor before they go in.
  • Remove the first few tufts as soon as you see them.

Why it happened

BBA usually arrives on plants or decor and then takes off when CO2 swings up and down, flow is weak, lights are old or on too long, or there's extra waste in the tank. In planted tanks with injected CO2, swings in CO2 are the most common trigger. It's also often found right in the path of the filter outlet, where nutrients and CO2 flow past.

When to get help

Ask for help if you've fixed CO2, flow and light and it still spreads, or if a treatment harmed your fish or shrimp. A planted-tank club or an experienced aquascaping shop can usually spot the cause from photos of your tank and equipment.

In the game

Multiple Tank Syndrome doesn't have a black beard algae card yet. The related card is "Algae takeover", which only an algae eater can clear.

Sources

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