Dark, bristly tufts on the edges of your Anubias leaves, your driftwood or your filter pipes? That’s black beard algae (BBA), and it’s one of the most stubborn algae in the planted tank hobby. It won’t scrub off like green algae and it rarely dies back on its own. The good news is that it’s predictable: BBA almost always points to the same few causes, and once you fix them it stops coming back.
What Is Black Beard Algae?
Black beard algae is a red algae, even though it looks black or dark grey in the tank. You’ll also see it called black brush algae. It grows in dense tufts a few millimetres long and grips so firmly to leaves, rock, wood and equipment that wiping it has no effect.
It usually appears first on slow-growing plants and hard surfaces — leaf edges of Anubias and Java Fern, the top of driftwood, filter inlets and outlets — because those surfaces stay in the tank long enough for it to establish.
BBA or something else?
- Black beard algae: short, dark, brush-like tufts. Feels firm and won’t pull off easily.
- Staghorn algae: greyish, stiffer strands that branch like antlers.
- Hair algae: soft, bright green threads that pull away easily. See our guide to getting rid of hair algae.
What Causes Black Beard Algae?
BBA isn’t bad luck. It thrives on instability, and the most common cause by far is carbon that rises and falls through the day.
1. Unstable or low CO₂
In tanks with pressurised CO₂, BBA is a classic sign that levels are swinging — the gas switching on too late, a cylinder running low, a diffuser in the wrong place, or CO₂ being turned off for weekends. Your plants can’t keep up with the light, and BBA fills the gap.
2. Carbon swings in low-tech tanks
Tanks without CO₂ get it too. Fresh tap water often carries more dissolved CO₂ than tank water, so very frequent or very large water changes can create the same up-and-down pattern that BBA exploits.
3. Poor water flow
BBA almost always starts in dead spots: back corners, behind hardscape, under broad leaves and around the filter. If water isn’t moving through an area, CO₂ and nutrients aren’t reaching the plants there either.
4. Organic waste and patchy fertilising
Rotting leaves, uneaten food and dosing fertiliser in fits and starts all add to the instability. Consistency matters more than quantity.
5. Hitchhikers on new plants
BBA can arrive on new plants and wood. Check every addition before it goes in, or choose tissue culture plants, which are grown in sterile lab conditions and arrive free of algae, snails and pests.
How to Remove Black Beard Algae: Step by Step
Step 1: Remove what you can by hand
Trim off badly affected leaves at the base with a pair of Superfish Aquarium Plant Scissors — heavily covered leaves won’t recover cleanly, and the plant will replace them. Take affected rocks and wood out and scrub them with a stiff brush, away from the tank. Do this before a water change so you can siphon out any loose fragments.
Step 2: Spot-treat with liquid carbon
This is the most effective way to kill BBA that you can’t remove by hand. Turn off your filter, then use a syringe or pipette to apply a liquid carbon such as Neutro CO₂ Liquid Carbon or Easy-Life EasyCarbo directly onto the tufts. Leave the filter off for around 10 minutes, then switch it back on.
Treated BBA usually turns pink, red or white over the following days as it dies. Once it changes colour, it’s much easier to brush away, and fish and shrimp will often graze on it.
- Don’t exceed the total daily dose on the bottle for your tank volume — spot-treating counts towards it.
- Some plants, notably Vallisneria and certain mosses, are known to react badly to liquid carbon. Avoid treating close to them.
- Repeat every two to three days until the BBA has changed colour.
From Aqua Essentials
Neutro CO₂ is our go-to liquid carbon for BBA spot treatment, and for steady daily carbon in tanks without pressurised CO₂. Available in 500ml, 1L and 2L.
Shop Neutro CO₂ Liquid Carbon →Step 3: Stabilise your CO₂
This is the step that stops BBA returning. If you inject CO₂, use an Aquarium CO₂ Drop Checker filled with Neutro Bromo Blue. It should read green by the time your lights come on and stay green through the photoperiod. Set your CO₂ to start an hour or two before lights-on, and avoid switching it off for days at a time.
If you’re not injecting CO₂, dose liquid carbon every day at the same time rather than now and then, and keep water changes regular and moderate rather than large and sporadic.
If unstable carbon keeps causing problems and you’re running bright lighting, a pressurised system such as the Colombo CO₂ Profi Set 800g gives you steady, controllable CO₂. You’ll find diffusers, indicators and spares in our CO₂ accessories.
Step 4: Fix dead spots in your flow
Look at where the BBA is growing — that’s where your flow is weakest. Angle the filter outlet so the water travels the length of the tank, clear anything blocking it, and add a circulation pump if needed. In a well-flowing planted tank you should see gentle movement in every plant, including the back corners. For larger tanks, the Newa Circulation Wave Pump 3200 l/h is designed for planted aquariums of 150–350L. See our full range of circulation pumps.
Step 5: Feed consistently
Healthy, fast-growing plants are your best defence. Dose a complete fertiliser on a regular schedule: Neutro+ for tanks with pressurised CO₂, or Neutro T for low-tech tanks without it. Keep on top of dead leaves and excess food so organic waste doesn’t build up.
What Eats Black Beard Algae?
Very few animals eat established BBA. A group of Amano shrimp will graze softer, early growth and are excellent all-round algae eaters, but they won’t clear a mature outbreak on their own. The true Siamese algae eater (Crossocheilus) is the fish most often recommended for BBA, but it grows large and suits bigger tanks.
The most reliable approach is to treat clean-up crews as a help, not a cure. Fix the cause, spot-treat, and let your shrimp and fish tidy up the dying algae afterwards.
Black Beard Algae Treatments and Removers
BBA is resistant to most whole-tank algae treatments, which is why targeted liquid carbon is the usual first choice. General treatments such as Easy-Life AlgExit can help knock back algae while you fix the underlying cause, but no product will stop BBA returning if CO₂ and flow are still unstable. Always follow the dosing instructions on the label, especially if you keep shrimp or snails.
Some aquarists use hydrogen peroxide to spot-treat BBA. It works, but it’s much less forgiving of dosing mistakes and can harm shrimp, fish and delicate plants. We’d recommend trying liquid carbon first.
How to Stop BBA Coming Back
- Keep CO₂ stable — same start time every day, no weekends off.
- Check your drop checker regularly, not just when something goes wrong.
- Keep the flow strong and clean filters and pipes so flow doesn’t drop off over time.
- Water changes: regular and moderate (around 25–30% weekly) rather than large and irregular.
- Fertilise on a schedule, not when you remember.
- Add plant mass with fast-growing aquarium plants and floating plants to outcompete algae.
- Inspect new plants and wood before they go in.
Black Beard Algae FAQs
Is black beard algae harmful to fish? No. BBA isn’t toxic to fish or shrimp. The problem is that it smothers slow-growing plants and looks untidy.
Will black beard algae go away on its own? Rarely. Even after you fix the cause, existing tufts usually need trimming or spot-treating. New growth should stop once conditions are stable.
Why has my BBA turned red or pink? That’s a good sign — it usually means the algae is dying after liquid carbon treatment. It should become easy to brush off.
How long does it take to get rid of BBA? Spot-treated tufts typically change colour within a few days. Stopping new growth depends on how quickly you stabilise CO₂ and flow — give it a few weeks before judging.
Why does BBA grow on my filter pipes? Filter inlets and outlets see a lot of passing nutrients and are rarely cleaned. Scrub them during maintenance, and treat growth there as a sign to check your flow and CO₂.
BBA is a symptom, not a mystery. Stabilise your carbon, fix your flow, feed consistently and spot-treat what’s already there, and it won’t come back. Need help working out what’s causing it in your tank? Get in touch — we’re happy to help.
