What are the black spots on my aquarium plantBlack spots on aquarium plants can be easily treated if you know the exact reason why they appeared. Many things can contribute to this condition, so experimenting with different remedies without knowing the actual cause will do more harm than good. To help you out with that we have created this comprehensive guide on how to identify causes, remove, and prevent that black stuff on aquarium plants.

What Are the Black Spots on My Aquarium Plant?

The primary reason for black spots on the leaves of aquarium plants is Black algae. But, usually, people new to fishkeeping assume the black dots on aquarium plants as a plant disease that will kill their plants. However, they are not always due to an aquarium plant disease.

Black Bread Algae

Black Bread algae can appear in different shades such as black, dark gray, and very dark green. It leads to the formation of tiny spots on aquarium plants’ leaves, especially on leaves’ edges. The algal growth begins from edges and expands all over the plant surface if not checked early.

When the black algae have reached maximum growth, fluffy tufts appear on the plants’ surface. These algal clusters resemble the surface of a brush or bread; hence black algae is also commonly known as black bead algae. Moreover, the black spots that it leaves on aquarium plants can go away by changing some parameters required for plant life in the fish tank.

What Causes Black Algae on Aquarium Plants?

The possible causes of Black algae on aquarium plants are:

Excess of Nutrients

Aquarium plants need nutrients for proper growth. Essential nutrients that plants need for optimal development are nitrogen, potassium, and phosphorus. But when used in excess of they can promote black algae in aquariums.

In the presence of excess nutrients, especially phosphates, the rate of photosynthesis increases. What’s more, the increased rate of photosynthesis can promote algal growth too.

Carbon Dioxide Levels

Like nutrients, the excess of carbon dioxide also favors black algae growth. All the chlorophyll-containing organisms, including black algae, use photosynthesis for growth. Carbon dioxide is a substrate for the reaction of photosynthesis. So, in the case of both low and high carbon dioxide levels, you’ll see black dots on aquarium plants that are actually black algae.

When the carbon dioxide is less than a specific limit, plants can’t absorb it and use it for photosynthesis. However, black algae are really good at detecting and absorbing even low levels of carbon dioxide. Hence, the growth of black algae occurs in both conditions. Saying that, the growth will be more when the carbon dioxide levels are low due to less growth of aquarium plants.


Both plants and algae grow when adequate light is available. But algae can also grow in low light. So, if the light levels drop, the photosynthesis and growth of aquarium plants will stop. Black algae will take advantage of this situation and speed up its growth.

How To Get Rid of Black Spots on Aquarium Plants?

Fortunately, there are many ways you can get rid of black spots on aquarium plants, including:

Dip Affected Plants in Hydrogen Peroxide

Hydrogen peroxide is a readily available chemical that can be used to remove black algae from aquariums. All you have to do is take three percent of hydrogen peroxide and soak the affected plants in it for two to three minutes. After that, you can wash your plants with clean water to get rid of the hydrogen peroxide.

Regulate the Quantity of Phosphates in Your Aquarium

Whenever something decays in your aquarium, phosphates are released. In the presence of high levels of phosphates, black algae can grow rapidly. Therefore, you must reduce the quantity of phosphates in your aquarium to get rid of black algae.

Increase the Levels of Carbon Dioxide

The increased carbon dioxide levels will promote the photosynthesis of plants. With an increased rate of plant photosynthesis, the competition for nutrients will increase in the tank. Plants will absorb most of the tank nutrients, depriving the algae of essential nutrients it needs for survival. Consequently, its presence in the tank will be reduced.

Add Black Algae Eating Fish to Your Aquarium

The most commonly used black-algae-eater fishes are Siamese Algae Eaters (SAE is the abbreviation). These algae eater fishes feed on algae and reduce their number in the fish tanks. This method of removing black algae is combined with hydrogen peroxide to increase carbon dioxide in the aquarium.

Both hydrogen peroxide and carbon dioxide make the algae weak. Thus, it becomes easy for the algae eater fishes to attack and destroy the algal growth.

How Does Black Algae Get Into the Fish Tank?

Black algae aren’t produced in the fish tank. The spores of the algae are introduced from outside, usually on the surface of contaminated plants. Guts of fish can also be a source of black algae. No matter how the spores come into the aquarium, black algae can’t grow if suitable conditions for growth are not available.

Is Black Beard Algae Harmful to Fishes?

No, black beard algae aren’t harmful to fishes. In fact, many fishes enjoy the presence of black algae in the aquarium. It’s because they use the algae for hiding. Moreover, many fishes also collect the leftover food particles that become trapped in the beard of the black algae.

However, it can harm the fish indirectly. Due to black algae, the tank environment changes considerably and becomes unstable for fishes.

Are Black Beard Algae Harmful to Aquarium Plants?

Yes, black bread algae are harmful to aquarium plants. However, it uses an indirect route to harm them. Both algae and plants need the same nutrients for survival. So, if algae grow on the plants, competition for resources will start.

Initially, when the algae don’t have significant growth, no problem occurs. The issue begins when algae expand and start consuming most of the light and nutrients in the tank. Aquarium plants often die due to the absence of food if algae remain in the water for too long.

How To Prevent Black Algae Outbreak in Your Fish Tank

What causes black algae on aquarium plantsWe think that the ultimate way to reduce black algae in your tank is to prevent it in the first place. There are many ways that you can use to avoid black algae outbreaks in your fish tank, like:

Reduce Light Levels in Fish Tank

All algae, including black bread algae, can flourish rapidly in the presence of light. Your tank will have abundant algal growth if your aquarium receives a lot of light for a major portion of the day.

To avoid this, reduce the light that your tank receives to eight hours a day and cover your fish tank to protect it from direct sunlight. This way, you will not see any black algae in your tank; even old algae will disappear with time.

Ensure Proper Maintenance

To prevent the growth of black algae in your tank, it’s crucial to consistently keep an eye on the tank’s maintenance. Moreover, the conditions of your tank should not favor the growth of black algae. These conditions include lower phosphates, proper filtration, and regular water change.

Regularly Check Carbon Dioxide Levels

As lower carbon dioxide levels encourage black algae to grow, make sure the amount of carbon dioxide remains high in the tank. You can do this by putting carbon-containing compounds, such as flourish excel, in water.

Add More Live Plants in Your Aquarium

Live plants in your aquarium use nitrates as fertilizer, so keep the water clean, since algae can’t grow in clean water. Moreover, the abundance of live plants creates competition for nutrients. These plants don’t allow the algae to consume more nutrients in the tank. As a result, the growth of the algae stops or is very limited.

Clean New Plants

Clean your new plants with hydrogen peroxide before putting them in your aquarium since it kills the harmful bacteria and algae that may be present on their surface. There is no waiting time to put your plants into the tank after washing them with hydrogen peroxide.

Keep New Fishes in Quarantine for Some Time

Whenever you get new fishes for your aquarium, keep them in quarantine for some time. It will help you to separate the fishes that may have a disease or carry algae spores. It reduces the risk of black algae outbreaks in your fish tank.

Always Purchase Tank Items From Reputable Stores

Always purchase plants, fish, or décor items for your fish tank from reputable stores, since they quarantine their items before selling them. This way, you can ensure that you have got things free from any infections and algal spores.

Never put anything in your aquarium from the natural environment. The natural habitats may contain various pollutants and infectious particles. By putting plants or fishes from natural habitats into your aquarium, you can increase the risk of algal blooms and other problems in your tank.


Black spots on aquarium plants can confuse you, especially if you’re a new aquarium hobbyist. But now you know the essential things given below to keep your aquarium safe from the black fuzz on aquarium plants:

  • The black spots on aquarium plants are due to the presence of black beard algae
  • Excess of nutrients, light, and carbon dioxide favor algal growth.
  • You can control algal growth by altering the conditions of the aquarium.
  • With a proper aquarium maintenance routine, you can prevent the outbreak of Black algae in your aquarium.

Black spots on aquarium plantsKeep a close check on your aquarium plants and when you see the black dots on them, start their treatment. Even if the spots aren’t there, you shouldn’t forget prevention can save your aquarium plants!

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