Aquarium Plants Turning Black: All Reasons & Solutions

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It can be disheartening when your beautiful green plants end up turning black after a while. I remember a few months back when I noticed my plants turned black on the leaves. My fish was still alive, but the plants looked awful. As time passed, I learned why that was happening and how to fix the issue.

Aquarium plants tend to turn black when algae grow on their leaves, most commonly Black beard algae. That typically happens when the aquarium is exposed to too much light or not cleaned regularly. However, aquarium plants also turn black due to nutrient deficiency, including iron and phosphate.

As we move forward, I will take you step-by-step through the process of how to get rid of algae and maintain healthy aquarium plants. Following this guide, your plants will retrieve their original colors within a few weeks.

Why Are My Aquarium Plants Turning Black?

Most aquarium plants are green. If yours are turning black or even brown, most people will blame the issue on poor maintenance. However, poor maintenance cannot explain every single instance in which aquarium plants turn black. On occasion, one or more of the following is to blame:

1. Black Algae Grew On Your Plants

Black beard algae is a nuisance. Also known as brush algae, the black beard alga comes in various shades of gray, dark green, and black.[1] People tend to ignore the algae when it first appears because it manifests as small, seemingly harmless spots along the edges of a plant’s leaves.

Over time, it becomes fluffy tufts that eventually spread, encompassing the rocks, filters, driftwood, and every other object in the aquarium. Black beard alga is not dangerous to fish.

In fact, many aquarists will incorporate the species into the design of their aquatic environment, removing just enough black algae to prevent the infestation from choking their tank. 

If left unchecked, black algae will cover your plants, blocking access to sunlight and vital nutrients. Take a closer look at the black substance on your plants. If it looks like fluffy tufts, like a brush, you have black beard algae.

You can introduce the species to your tank via contaminated plants and decorations. Low levels of CO2, poor water circulation, and intense lighting can encourage the algae to spread.

2. Your Plants Aren’t Getting Enough Nutrients

Plants require macro and micronutrients to thrive. The absence of these nutrients can alter the color. For instance:

  • CO2 – inadequate levels of CO2 will give your plants a yellow color.
  • Phosphates – If the tank doesn’t have enough phosphates, the leaves will develop yellow patches before disintegrating. But you cannot rely on excess phosphate levels to solve the problem. Excess phosphates will turn the leaves black. If you don’t fix the problem, the plants will die.
  • Nitrogen – With insufficient nitrogen levels, the leaves may develop a yellow or reddish color.
  • Nitrates – Excess nitrates are harmful because the plant will turn brown or black before finally dying. You find high concentrations of nitrates in tanks that haven’t been cycled to completion. As such, they don’t have enough good bacteria to process the waste products aquarium creatures produce.
  • Iron – New leaves will turn yellow in an iron-deficient tank. Mature leaves will become transparent with green veins. But that is only true in the early stages of iron deficiency. In advanced cases, the leaves will turn black before the plant dies.

3. The Plants Are Exposed To Too Much Light

Does your tank have sufficient light? You must avoid both extremes. If the tank doesn’t have enough light, the leaves will turn a pale color. 

But if you have too much light, the plant may develop dark patches and colors before wilting. In the worst-case scenario, excess light will enhance the growth of black and brown algae, choking your aquarium’s foliage.

4. Your Plants Are New To Their Environment

If your plants were grown above water, they might respond negatively to the conditions in the tank. Some plants will recover if you give them enough time. They may melt at the start, but that only serves to eliminate the leaves they grew above water.

Over time, they will grow new leaves that can survive underwater. You just have to wait.[2] Don’t be so quick to remove the plants simply because you noticed some black and brown patches. This assumes that you planted the foliage correctly, giving it suitable fertilizers, nutrients, and substrate.

Different aquatic plants have different requirements. You have to install them correctly to prevent the plants from dying. For instance, floating plants are the least challenging because you can just place them on the surface of the water.[3]

On the other hand, you must place bulb plants on the substrate. The roots will organically descend into the substrate. With bare root plants, you have to trim the roots before planting the individual plantlets.

Aquatic plants are no different from the species you plant above water. If you install them poorly, they will change color and wilt.

How Do I Get The Black Stuff Off My Aquarium Plants?

If your plants are turning black, you must act quickly. Left untreated, your plants could die. Fortunately, aquarium plants are durable, and they will most likely recover once you eliminate the factors responsible for their discoloration. Some of the practical solutions you can try include:

1. Adjust The Lighting For Aquarium Plants

Aquariums require a regular day/night cycle. Don’t give your plants more than 12 hours of light on any given day. You should also limit the tank’s period of darkness to 8-12 hours. If you have artificial lighting, you don’t have to rely on sunlight. 

I also suggest keeping the aquarium away from windows. Direct sunlight benefits algae. If you don’t have algae, direct sunlight will cause it to manifest. If you have algae, the infestation will get much worse.

As far as the quantity of light is concerned, try to match the lighting to the size of the tank. For instance, a single 15W tube is more than adequate for 10 gallons. In a 20-gallon tank, you can use one 30W tube or two 15W tubes. Forty gallons require two 30W tubes, whereas 84 gallons should be paired with three 40W tubes.[4]

2. Take Care Of The Environment

Like fish, plants require proper care, not just in the initial stages of introducing them but in the weeks and months that follow. Keep the following in mind:

  • Don’t crowd the tank with plants. Not only do you reduce the space available to the fish, but the plants may fight for resources. Those that lose will die.
  • Add 2-3 inches of a substrate to the bottom. Try to match the type of substrate to the type of plant. Some plants don’t appreciate gravel.
  • Take the requirements of each plant into account before you add it to the tank. For instance, you have to bury some plants in the gravel to the base of the stem. Others should be left on top of the gravel.
  • Fish require water changes, but so do plants. Perform water changes of 10 percent every week. If you want to change the water monthly, aim for 25 percent. Without proper water changes, the water will get dirty as it accumulates waste and debris. 

Many aquarists prefer to maintain tanks with filters. But a filter cannot keep a tank clean, not on its own. A dirty tank will kill all your plants. But before that happens, their leaves will change color. To save your plants from such untimely deaths, perform regular water changes.

  • If you want to reach into the tank to remove waste, fix the heater, move the decorations, etc., start by thoroughly washing your hands. Your hands may introduce contaminants to the water, which is the last thing you want. 

Use ordinary washing soap. Sophisticated detergents may stick to your hands despite thorough rinsing. Those sophisticated detergents have chemicals that are more than capable of killing your fish and plants. 

After interacting with the tank and its contents, you should also wash your hands. You don’t want to infect yourself or other people with germs.

3. Provide Your Plants With Nutrients

If you suspect that your plants aren’t getting enough nutrients, I highly recommend checking the Seachem Flourish Tabs Growth Supplement (link to Amazon). All you have to do is scatter these tabs 4 to 6 inches from each other. Here is an excellent Youtube video that shows how to do that:

As a rule of thumb, you’ll require about six tabs for every 10 gallons of water. By adding those, you’ll elevate essential nutrients. That includes Nitrogen, Phosphate, Calcium, Magnesium, Iron, Manganese, etc.

The advantage of nutrient deficiencies is that they are relatively easy to solve. If you wish to treat each nutrient separately, you can use these test kits:

After testing the different components, you can take the necessary steps to fix them:

  • Nitrogen – If you have a nitrogen deficiency that has turned the plants black or brown, make sure the tank is fully cycled. If it isn’t, cycle the aquarium to completion. You can expedite the process by getting filter media from an established tank and adding it to yours. 

If your aquarium is cycled, but the nitrogen deficiency has persisted, add liquid fertilizers like Seachem Flourish Nitrogen (link to Amazon) that are rich in nitrogen.[5]

  • Phosphorus – If you have too many phosphates in the tank, perform a water change.
  • Potassium – If the plants have black dots and holes because of a potassium deficiency, add a liquid fertilizer and root tabs.
  • CO2 – You can overcome carbon dioxide deficiencies with carbon injection systems.

Fertilizers are the answer to most nutrient deficiencies. But you should match the fertilizer to the deficiency. Some fertilizers are designed to inject specific nutrients into the tank.

4. Get Rid Of Black Algae

To remove black algae, you have to start by performing regular water changes. Make sure you remove all the solid waste and vacuum the substrate. I also suggest adding a phosphate-removing resin to the filter. This will starve the algae.[6]

A more straightforward solution involves the use of hydrogen peroxide. Three percent H2O2 Hydrogen Peroxide (link to Amazon) will kill black beard algae. You can soak the individual plants (rinse them thoroughly) or treat the entire tank.

If you don’t have the time or the means to remove the affected plants, add the hydrogen peroxide directly to the tank. Deploy the product near the pump outlet to distribute it evenly. However, one treatment is not enough. 

You need to treat your aquarium for three days. It should only take a month for the algae to die. Some people recommend the heating method, but it only works on artificial plants. You can’t boil live plants in water because they won’t survive.

It might be easier to introduce creatures such as Amano shrimp that eat algae if you have the room, as I explained in this article. Though, you need a large population of algae eaters to control the algae in the tank.

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Aquarium plants usually turn black because of algae growth and nutrient deficiency. If you have an algae problem, perform a water change and add a three percent H2O2 Hydrogen Peroxide solution. Bear in mind that this process takes time.

If a nutrient deficiency causes the black shades on your plants, boost their nutrition by adding fertilizing tablets to the substrate. Within two weeks, you should see an improvement, assuming you’ve added enough nutrients.