Black beard algae: how to get rid of BBA in a planted tank

Black beard algae (BBA) is a red alga that forms dark, bushy tufts on leaf edges, driftwood and stone. Few animals eat it and it does not come off with a wipe, so the usual approach has two parts. Kill the existing tufts with 3% hydrogen peroxide or a liquid carbon product, then fix the light, CO₂ and nutrient balance that let it grow. Aquarium Co-Op warns that BBA can take six to eight months to establish and that getting rid of it takes at least as long.

What black beard algae looks like

Buce Plant identifies it as a form of Audouinella, a genus of red algae, also sold under the names black brush algae and black algae. Despite the name, the tufts can be black, grey, dark green or dark red. It grips leaf tips, wood and rock, and it often appears where water flow is strong.

Aquarium Co-Op describes it as one of the most troublesome algae in the hobby because so little eats it. Left alone, it can cover an aquarium in one to two years.

Why it grows

Both sources say there is no single cause. Buce Plant lists the usual suspects:

• too much organic waste from overfeeding, overstocking or skipped maintenance;
• more fertilizer than the plants use;
• CO₂ that is low, or injected CO₂ that rises and falls from day to day;
• too much light, in intensity or in hours.

Buce Plant explains that when CO₂ runs short, BBA can pull carbon from bicarbonate in the water more easily than plants can. The plants slow down and leave nutrients unused, and the algae takes them.

BBA does not harm fish or shrimp. The risk is to plants: a leaf completely covered in tufts loses light and can die.

How to kill it

Treating the tufts removes what you can see. Both sources say it comes back unless the cause is fixed.

Hydrogen peroxide

Aquarium Co-Op uses plain 3% hydrogen peroxide from a drugstore. Lower the water until the affected plants and decor are above the surface, spray the algae, wait 5 minutes and refill. A piece of wood or a plant can also be taken out and treated outside the tank. For delicate plants, shorten the contact time or treat a small part first.

Buce Plant gives roughly 1.5 ml of 3% peroxide per gallon as the amount when spot treating underwater with a syringe. It recommends switching the filter off before treating and leaving it off for 15 minutes to an hour, because peroxide can damage the bacteria in the filter.

Treated tufts turn red, pink or clear. Aquarium Co-Op notes that animals may eat the algae once it is weakened, and Buce Plant suggests leaving the dead tufts to algae eaters if brushing them off would damage the plant.

Liquid carbon

Glutaraldehyde-based liquid carbon slows BBA in the whole tank and kills it when applied directly. Buce Plant describes two ways: drip it onto the tufts with a pipette, or soak removed plants and decor for 24 hours in water dosed at twice the label rate, follow with 24 hours in clean water, then repeat the cycle once. It warns that some plants react badly to liquid carbon, naming crypts and vallisneria, such as Cryptocoryne wendtii ‘Green’ and jungle val.

Trimming

Cut off leaves that are heavily covered. Buce Plant points out that removing them stops the leaves decaying in the tank and adding more waste.

Animals that eat BBA

Both sources name Siamese algae eaters, Florida flagfish and Amano shrimp. Buce Plant adds nerite snails and notes that Siamese algae eaters can reach about 6 inches. Aquarium Co-Op adds that Amano shrimp are slow at it unless there are many of them. They are most useful on algae already weakened by treatment, and the cause still needs fixing.

How to keep it from coming back

• In a tank with injected CO₂, Buce Plant recommends running it for the same hours and at the same rate every day, checked with a drop checker.
• Buce Plant suggests no more than 6 to 8 hours of light a day, or a dimmer if the light is strong.
• Plants compete with algae for the same nutrients. Fast growing aquarium plants, stem plants and floating plants use more of them than slow growers such as anubias. In the catalog, water wisteria and Ludwigia repens are rated fast and grow without added CO₂.
• Change water and vacuum the gravel weekly, as Buce Plant recommends, to remove waste before it breaks down.
• Feed less. Buce Plant says fish are fine with one feeding a day.
• Match fertilizer to the plants. See aquarium fertilizer and root tabs for which plants need it in the water and which through the roots.
• Buce Plant recommends quarantining or bleach-dipping new plants, or buying tissue culture, and cleaning tools before using them in another tank.

Frequently asked questions

Is black beard algae harmful to fish?

No. Buce Plant says it poses no threat to fish or shrimp. It can kill a plant by covering its leaves.

How long does it take to get rid of BBA?

Aquarium Co-Op’s rule of thumb is that it takes at least as long to remove as it took to establish, which it puts at six to eight months.

Why does BBA keep coming back after treatment?

Peroxide and liquid carbon kill the tufts but leave the cause in place. Unstable CO₂, long or strong light, excess nutrients and decaying waste are the usual reasons it returns.