What Are the Black Spots on Aquarium Plants? (FAQs)

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If you’ve discovered some black spots on your live plants, you may be concerned that there’s a problem to be addressed. In many cases, you’d be right. Black patches growing on aquarium plants is often due to ‘black beard algae’, a problematic type of algae that can overwhelm your aquarium if not dealt with urgently.

Other times, black patches on plants may simply be due to nutritional deficiencies or incorrect aquarium lighting. Here we’ll look at the causes of the black spots on aquatic plants, as well as some ways you can rectify the problem.

What Is Black Beard Algae?

Black beard algae (Audouinella sp., Rhodochorton sp.) belongs to the red algae family, which gives us a clue to its other colors – it’s not always black!

These algae can also be red, brown, gray, or dark green. Other common names for this variety include black spot algae, brush algae, or simply ‘black algae’.

It first appears as spots on aquarium plants, rocks, driftwood, and décor. As it develops, it becomes fluffy or fuzzy, giving it the name black beard algae, or black brush algae (it’s also often abbreviated to BBA).

How Did Black Beard Algae Get Into My Fish Tank?

Black beard algae reproduce by microscopic algae spores. Because these spores are so tiny, they can travel around without detection.

They can pass from one fish tank to another when plants, aquarium ornaments, or even fish are moved between tanks. If you see black spots on an aquarium plant in a pet store, please don’t be tempted to buy it! BBA is much more difficult to remove than prevent– it’s always better to try avoiding it in the first place.

Sometimes, black beard algae can lie dormant within a fish tank for long periods, waiting for the right light, CO2, and nutrient levels for its emergence. If you have a black algae outbreak, changing these conditions is often a key to removing it.

In What Conditions Does Black Beard Algae Grow?

Black beard algae grow rampantly when an aquarium is suffering from poor water quality. High nitrates and phosphate levels from overfeeding, overstocking with fish, and poor tank management are typical causes for blooms of several types of algae.

Can Black Brush Algae Kill My Plants?

anubias plant leaf in aquarium

Yes, if BBA completely covers the leaves of your plants, they won’t be able to photosynthesize any longer and will die off.

This is one of the reasons why this type of algae is often considered to be such a menace in aquariums and should be removed as soon as it’s discovered.

How Do I Get Rid of Black Spot Algae?

To get rid of black spot algae growth, you need to find a way to remove the bulk of it, and also correct the underlying causes of its rapid growth to prevent it from growing back.

Removing Black Spot Algae By Hand

Like other algae, black spot can be scrubbed by hand, treated with a hydrogen peroxide bath, a weak bleach solution, or a specialist product such as Seachem Flourish Excel, which can be used as a herbicide in high doses.

You need to be very careful about using these chemicals in your aquarium, though, as they can also impact the health of your fish and live plants.

In fact, some aquarists avoid such chemicals altogether to guard against the potential health risks to their livestock.

If you do choose to use chemicals, research the methods thoroughly to avoid disaster. Nobody wants to have dead fish on their hands from applying the wrong treatment.

No matter what manual treatment you try, black beard algae is stubborn and notoriously difficult to get rid of, so you may do well to find some algae-eating pets to help you in solving the problem.

Fish and Invertebraes That Eat Black Beard Algae

Personally, I’m not a big fan of chemical intervention and tend to prefer biological solutions to biological problems. If you have an algae infestation, find an algae eater that will eat that type for you!

Black beard algae is less popular with many algae-eating fish than other types of algae, but thankfully some species will still eat it:

Fish That Will Eat BBA

There are many myths about which fish will eat black beard algae. Many good algae eaters like plecos and Oto catfish will only eat it if they’re very hungry.

Flagfish, panda garra, and flying foxes have also been suggested, but looking through fish keeper’s reports, these species seem to prefer other types of algae before they’ll take on old captain black beard!

The best eater for black beard algae appears to be the Siamese algae eater (Crossocheilus oblongus). Unlike its cousin, the Chinese algae eater, the Siamese algae eater (aka. SAE) is a peaceful fish that enjoys being kept alone or in groups.

These helpful cleaner fish are the only species that I’ve come across that seem to actually relish eating black beard algae. There are many reports of delighted aquarists watching their SAE hoovering up large quantities of the black fuzz – at last, a real solution!

Invertebrates That Will Eat BBA

A bit like many algae-eating fish, most invertebrates seem to only eat black brush algae when forced!

Pagoda snails, nerite snails, ramshorn snails, and Amano shrimp have all been reported to eat BBA, but if you look a bit deeper into the details, that’s only when they don’t have other food available.

Overall, the Siamese algae eaters appear to be the top pick for cleaning up black beard algae!

Correcting Water Parameters to Reduce Black Beard Algae

Improve Water Quality

Since black beard algae thrives in poor water quality, one of the best measures you can take to reduce it is improving your tank hygiene.

Avoid overfeeding, and always remove any fish food that’s left uneaten after a few minutes to prevent it from contaminating the water.

Make partial water changes with clean water, vacuum your gravel, and clean your aquarium filter regularly to reduce the high levels of nitrates and phosphates that can cause algae blooms.

Change Your Lighting

Over-intense or incorrect spectrum lighting can cause blooms of BBA. Therefore, consider changing your lighting setup to an intensity and spectrum that’s favored by your plants, but not algae.

The great news is that many aquarists have reported successfully defeating their black beard algae in this way!

If you’re unsure how to adjust the light properly, consult your local specialist pet store to learn which lighting would be the best for your particular setup.

Change Your CO2 Concentration

Black spot algae loves conditions with fluctuating, irregular carbon dioxide levels.

If you’re using a CO2 injection system, try to keep your CO2 levels balanced and in the right quantities to feed your plants without feeding algae.

Other Causes of Black Spots on Aquarium Plants

Black spots on your plants might not be black spot algae. If the black spots on your plants remain fairly smooth and flat without becoming hairy, then it’s caused by something else.

Just as we can get different types of blemishes on our skin, aquatic plants can get different kinds of spots on their leaves. If your plants aren’t receiving the right nutrients and environment conditions, various color changes and blemishes can occur.

Black spots on java fern, for example, can be caused by a potassium deficiency, or not enough dissolved CO2 in proportion to the lighting intensity in the tank.

Plant leaves can also turn brown or black when the lights are simply too strong for them, or when they’re moved from one tank to another with different conditions.

A common example is with Amazon sword. This plant is often grown in a humid atmosphere rather than submerged in water in pet stores.

When you submerge it in your tank, the old leaves will turn brown or black and die, as it grows new, thinner replacement leaves that are better adapted for life underwater.

Correcting Tank Parameters For Healthy Plant Growth

Since black spots often indicate a problem with your plant’s health, you can remedy it by correcting certain parameters.

If you suspect the problem is caused by a lack of nutrients, try placing some root tabs in the substrate where your plants are growing.

If the plants have been scorched by lighting that’s too strong, change your bulbs to a dimmer intensity. To find out if your tank is lacking enough dissolved CO2, get yourself a CO2 drop checker and install an injection system if necessary.


Black spots on aquarium plants are often associated with black beard algae, a troublesome type of algae that should be removed as soon as possible. Getting a Siamese algae eater and altering your aquarium lighting are probably your greatest allies for getting rid of it!

Other causes for black spots on plant leaves include insufficient plant nutrition, lighting, and CO2 levels, and can be corrected by improving these conditions.

I hope that some of these suggestions have given you some useful ideas on how to correct these various issues so that you can enjoy your plants returning to a lush and healthy green color very soon!

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