Why Does Aquarium Gravel Turn Black? (How To Get Rid Of It?)

Image of an aquarium with gravel

Aquarium gravel is beneficial for fish and plants. However, seeing your gravel become dark can be disturbing. But why does aquarium gravel turn black?

Aquarium gravel usually turns black due to black beard algae bloom. Other reasons are low carbon dioxide levels in the tank water, increased phosphate levels, and excessive lighting. Introducing algae eaters, boosting carbon dioxide, and hydrogen peroxide treatment controls black algae infestation.

Moreover, black beard algae can make the tank look unattractive. So, let’s talk about this in detail now.

2 Main Reasons Why Aquarium Gravel Turns Black And Ways To Stop It

The most common reason for the aquarium gravel to turn black is improper maintenance.

If you have an established tank, it’s essential to keep the water parameters in check and maintain good filtration.

This will help prevent your gravel from getting discolored or black.

Below are the two prominent reasons for aquarium gravel to turn black.

1. Black beard algae.

Black beard algae are one of the main reasons for aquarium gravel to turn black.

If you have an overgrowth of black beard algae on the gravel, this can cause the gravel to turn black.

These algae form because of too much nitrate and phosphate levels in the water.

Besides, black beard algae use nitrate as a food source. So, the increase in nitrate levels helps in the growth of algae.

Vacuuming the gravel regularly helps clean the black beard algae.

Another good way is to cut off their food sources such as nitrate, light, and phosphate.

Placing live plants that absorb nitrogen from the water also helps in reducing black beard algae growth.

Finally, adding algae-eating fish to the tank, such as Siamese Algae Eater or Shrimp, can fasten up the algae cleaning process.

2. Leftover food and fish waste.

Aquarium gravel can turn black if the uneaten fish food or debris is not cleaned regularly.

Also, fish feces that settle on the gravel often turn it black.

To avoid this issue, remove all the leftover food from the tank daily. Also, clean the gravel regularly before it turns black.

Recommended Further Reading:

What Causes Black Beard Algae?

Black beard algae is a common problem in tropical and temperate aquariums.

They initially appear as tiny dots on the edges of the plants. As they grow, they resemble a beard or brush.

Three primary reasons that cause black beard algae bloom in an aquarium are:

1. Carbon dioxide fluctuations.

Carbon dioxide (CO2) fluctuation is the primary reason for the overgrowth of black beard algae.

If the CO2 levels are low or unstable in an aquarium, it leads to black algae growth.

Varying CO2 levels can be a result of water changes.

If you perform a large water change, it can significantly fluctuate the CO2 levels.

When the CO2 is unstable, plants can’t use light and fertilizers to undergo photosynthesis.

Such an environment is conducive to the growth of black beard algae.

Another reason for low CO2 levels in an aquarium is an underpowered filter.

An underpowered filter causes poor water circulation that lowers the CO2 levels of the tank water.

If you have algae bloom due to CO2 fluctuations, then maintaining or adding CO2 to the tank water must be your top priority.

2. Excessive light.

Like any other algae, black beard algae thrive on light.

Therefore, they grow best when there is plenty of light available. The more the light, the faster they grow.

If you have a planted tank, the problem of black algae is more common. Aquarists install LED lights for plant growth.

These lights not only help the plants to grow but also help in the growth of algae.

So, the most important thing to do to prevent black beard algae growth is to keep the lighting conditions stable.

You can restrict the use of light to control black beard algae growth.

Usage of aquarium lighting timers is a great way to keep lighting conditions constant and correct.

3. Increase in phosphate levels.

Phosphates encourage black beard algae bloom in an aquarium.

Improper maintenance of the tank can lead to an increase in phosphate levels of the tank water.

Phosphate levels increase in the tank water when leftover fish food, fish excreta, and decayed materials are not cleaned regularly.

Alright! Now that you know the reasons of black algae bloom in an aquarium, let’s learn how to get rid of them.

Related Further Reading:

How To Get Rid Of Black Algae From An Aquarium?

Black algae can spread quickly and cover all gravel, decorations, plants, and aquarium equipment.

So, it’s crucial to control their growth before it’s too late.

Following are some effective ways to get rid of black algae from an aquarium.

1. Cut black beard algae immediately.

Cutting black beard algae can be effective only when they have started to appear in small numbers on the plants in the tank.

However, there is no guarantee that these algae will not grow again because it’s likely that some of the black beard algae are lurking in the tank that you have missed cutting.

So, you should take some effective steps to remove the black algae from your tank altogether.

2. Introduce algae eaters.

Introducing algae eaters is one of the easiest ways to remove black algae from an aquarium.

It’s beneficial to introduce algae eaters in the early stages of algae growth to control and reduce their bloom.

Also, you should not feed too much food to the algae eaters.

Otherwise, they will happily devour the food leaving aside the black algae.

Another vital thing to remember is that the algae eaters should be compatible with the tank inhabitants.

Some of the algae eaters that eat black algae are:

  • Siamese Algae Eater,
  • Chinese Algae Eater,
  • Amano Shrimp,
  • Cherry Barb,
  • Bristlenose Pleco,
  • Cherry Barb,
  • American Flagfish, etc.

3. Keep phosphate levels down.

Increased phosphate levels benefit black algae growth in an aquarium.

Hence, keeping the phosphate levels low is one efficient way to control black algae growth.

Phosphates are a byproduct of everything that decays in the aquarium.

Decayed material such as fish waste, uneaten fish food, fallen plants, detritus, etc., increase phosphates in the tank water.

Following measures can help keep the phosphate levels low in the tank water.

  • Remove the leftover food immediately from the tank before it rots,
  • Remove the fallen plant matter as soon as possible,
  • Do not overfeed the fish,
  • Maintain water quality by carrying out regular water changes.

Related Further Reading:

4. Boost carbon dioxide levels in the tank water.

Boosting the carbon dioxide levels of the tank water is another way to get rid of black algae.

Increasing the CO2 levels doesn’t directly eliminate the black algae but helps prevent them from growing.

If there are plants and black algae in the tank, both compete with each other to get the essential nutrients for them to thrive.

However, if the plants are supplied with sufficient carbon dioxide, they will outcompete the algae for nutrients.

The black algae will then starve and become weak. Subsequently, they will perish due to the lack of nutrients.

CO2 injection and Aerosol CO2 sets are the most effective ways of increasing carbon dioxide in the tank water.

5. Eliminate algae by heating the tank water.

Black algae thrive in warm water but not in hot water. So, heating the tank water is an excellent way to get rid of the black algae.

Before heating the water, you need to move the fish and live plants into another tank.

Also, clean the gravel to get rid of the fish waste and uneaten food before heating.

Then you can heat the water with the help of a heater to 110°F to 120°F (45°C to 50°C) and wait for some time.

The heat will burn the black algae and get rid of them completely.

You can then introduce the algae eaters to clear the fallen black algae.

6. Treat the tank with Hydrogen Peroxide.

Hydrogen peroxide treatment is used when the black algae infestation goes out of control.

You can treat the entire tank or only the affected objects separately.

For treating the objects, you can soak them in 3% hydrogen peroxide for about 3 to 4 minutes before rinsing in freshwater.

However, treating the objects separately can be difficult. Hence it’s advisable to treat the tank.

Also, it’s advisable to move your tank inhabitants to another container before treating the tank.

You can add 10 ml hydrogen peroxide per 15 gallons of water.

Also, ensure that you add flowing water. Then, repeat this process for three days.

Simultaneously, check whether the black algae color starts to fade.

If the algae color is fading, the treatment is effective, and you can get rid of black algae within a month.

On the contrary, if the tank is still suffering from black algae, you can repeat the process with a slightly higher dose of hydrogen peroxide.

Interesting Further Reading:

Are Black Algae Harmful To Fish, Plants, And Aquarium?

Black algae don’t harm the fish if their growth is in control. Many fish swim happily around the black algae.

Fish even look upon the black algae as a place to hide behind their long flowing hair.

However, if there is an overgrowth of black algae, it can be dangerous for the fish.

This is because black algae absorb oxygen from the water at night for respiration.

Moreover, black algae can cause an imbalance in the nutrient levels of the tank water.

This can prove detrimental to the overall health of fish.

Similarly, black algae in small quantities may not damage the plants.

However, if there is a bloom of black algae in the aquarium, it will affect the plants negatively.

As the algae spread excessively, they will cover the plants. This algae cover will deprive the plants of light and nutrients.

Without sufficient light, plants can’t photosynthesize and may perish due to starvation.

Similarly, excessive growth of black algae can affect water conditions.

Once the black algae reach a certain level, they can affect the water’s nutrient levels and harm the tank conditions.

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