How to Get Rid of Algae in Aquarium: Removal and Prevention Guide

Dr. Mollie Newton
Published by Dr. Mollie Newton PHD| Senior Editor
Last updated: June 6, 2024
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Numerous aquarium hobbyists frequently struggle with algae-related problems throughout their fish-keeping experience. This slippery substance is generally considered a nuisance in aquariums; it is not only unsightly but can also jeopardize the aquarium’s ecosystem and the well-being of the fish if not properly controlled.

Article Summary

  • Algae is a common issue in aquariums that can be unsightly, but it can also be beneficial for the tank’s ecosystem in moderation.
  • Different types of algae can grow in fish tanks, including brown algae, blue-green algae, red or beard algae, and green algae.
  • To prevent and control algae, you can take steps such as reducing lighting, controlling nutrient levels, performing regular water changes, and adding algae-eating fish and invertebrates.

Excessive algae is usually an indicator of an underlying problem in your aquarium, so it’s important to address it and identify the cause, otherwise, you could end up with a more serious issue on your hands.

If your aquarium has been struck with an algae outbreak, don’t panic! I’ve dealt with my fair share of this frustrating muck, so I’ll be going into everything you need to know about algae in aquariums to help you get rid of this troublesome gloop for good.

What Is Algae?

Clam Covered in Algae
Clam Covered in Algae

Algae is an umbrella term that refers to a diverse range of aquatic organisms that conduct photosynthesis. It’s found in both saltwater and freshwater, and contains chlorophyll like other plants, but it does not have true stems, leaves, roots, and vascular tissue.

Is Algae Bad for an Aquarium?

Aside from looking unsightly, algae is not bad for a tank – it’s actually beneficial for your tank’s ecosystem as it helps keep your water clean and serves as a vital food source for algae-eating fish species and invertebrates like the trapdoor snail. It also reduces toxic levels of forms of nitrogen in your water.

While some algae in a tank is perfectly normal and even healthy, an excess amount of it can cause issues.


Blue-green types (especially Anabaena and Microcystis) also produce toxins that can be extremely poisonous to fish, animals, and humans who are exposed to it.

Does Algae Produce Oxygen in Aquariums?

Algae converts carbon dioxide into oxygen during the day as part of photosynthesis, so yes, it does produce oxygen in aquariums. However, this process is reversed during nighttime hours.

When it’s dark, algae consumes oxygen and produces carbon dioxide. In tanks where there is excess algae and not enough aeration, this can make it difficult for fish to breathe. Furthermore, when it dies off, it also takes up oxygen, which can lead to suffocation in your aquarium inhabitants.

Is Algae Bad for Fish?

Algae itself is not harmful to fish, but an excess amount of it can be a sign that there isn’t something quite right with your tank.

Overgrown algae will compete for nutrients with any live plants in your fish tank, as well as reduce oxygen levels during nighttime hours.

Additionally, an algae bloom looks unattractive and will often emit a musty or earthy odor. Not only does this hinder the appearance of your aquarium, but it can also cause the room it’s located in to smell.

What Are the Types of Algae in Fish Tanks?

Aquarium with Algae
Aquarium with Algae

There are numerous types that can grow in fish tanks. I’ll be going over some of the most common types found in aquariums below to help you choose the best treatment methods to remove or control it.

Brown Algae

Also known as gravel or silica algae, brown algae isn’t actually an algae – it’s made up of billions of diatoms (microscopic creatures).

It usually starts as a single light to deep brown patch that looks soft and a bit like fine dust, often appearing on the substrate, aquarium walls, plants, and decorations.

It’s most common in new aquariums and typically appears during the cycling process. It’s completely harmless and can be easily wiped away manually or with a scraper. It normally disappears within a few months once the fish tank has matured.

Blue-green Algae

Blue-green algae or cyanobacteria (it’s also known as smear algae) are a phylum of photosynthetic bacteria that reside in wet soils and water. It’s usually caused by too much phosphate and low levels of nitrate in your water, as well as excess light and fish waste.


Cyanobacteria can be extremely harmful to fish, animals, and humans as they produce toxins called cyanotoxins. It’s impossible to identify whether a cyanobacteria bloom contains cyanotoxins, so you should always treat this bacteria with caution.

At first, blue-green is not very visible, but it grows rapidly and will look like blue or green mats on the surface of the water. It occurs naturally in ponds, lakes, canals, rivers, and reservoirs, but it can also appear in aquariums.


Manual removal and maintaining good water quality to remove excess nutrients can help. However, if your tap water contains high levels of phosphates or the substance is particularly thick, you may need to use an aquarium treatment like erythromycin to eliminate it.

Red or Beard Algae

Red algae is a red to purple color and usually appears as tufts on plant leaves and the edges of hard surfaces. It’s a type of cyanobacteria.

Black beard algae, alongside staghorn algae, belongs to the red algae family. It is a red, black, or grey color, and gets its name due to its resemblance to a beard. It is very common in planted tanks.

Unfortunately, all forms are difficult algae to remove with regular water changes and maintenance alone.


Hydrogen peroxide or bleach (5 to 10%) dips for a few minutes is one of the best ways for removing this substance from aquatic plants and tank decorations. Alternatively, you can use a red algae removal chemical treatment, which you should be able to find at pet stores or online.

Green Algae

Green algae is one of the most common types in aquariums, comprising of hair algae, spot algae, and thread algae, among others.

Most fish tanks will develop hair algae overgrowth at some point in time. It is harmless and a great food source for many fish and invertebrates. It is typically caused by too much light, either by direct sunlight or artificial light, alongside too many nutrients in the water. A natural way of removing hair algae is by introducing hair algae eaters to your tank.


Reducing the amount of light and nutrients your tank receives, manual removal, regular water changes, live plants, and algae-eating invertebrates and fish can help you control this algae overgrowth.

Green Water

Green water, also known as an algae bloom, makes your tank’s water look like pea soup. It’s caused by the growth of free-floating, single-celled phytoplankton. It grows extremely quickly and is hard to eradicate.

Compared to other algae types that can often be controlled via water changes or manual removal, these methods are seldom effective for green water.

Blocking off all light sources (including direct sunlight), using a diatomic filter, and an aquarium UV sterilizer are your best bet for getting rid of green water.


You should test your aquarium water to make sure ammonia, nitrite, nitrate, and phosphate levels are zero as high numbers of these will promote algae growth in your fish tank.

What Causes Algae in Aquariums?

Fish Near Filter Tube
Fish Near Filter Tube

Algae is caused by a number of factors, including an imbalance of or too many nutrients in the water, too much light, excess food, irregular water changes, and poor water quality. Nutrients, light, and water are all things it needs to grow and thrive.

I ran into a huge algae outbreak a few years back when I had my aquarium positioned next to a window (I also kept leaving my fish tank lights on for too long). As soon as I moved my aquarium to a darker location and remembered to switch my lights off during the evening, the problem resolved itself.

The reason behind an algae overgrowth in your tank could be as simple (and easily resolved) as this!

Will Aquarium Algae Go Away on Its Own?

Some species of algae will disappear on their own, while other algae species will require intervention from the fishkeeper to control and eliminate.

For instance, brown algae will usually go away within a few months, but other types will need to be manually removed or treated.

How to Get Rid of Algae in Aquariums

The best way to remove algae in aquariums depends on the type, but reducing lighting, decreasing or balancing nutrient levels, and maintaining good water quality all help control and prevent it from occurring.

Additionally, adding aquatic plants and fish or invertebrates that are algae eaters can keep this unappealing substance at bay.

Steps for Removing Algae

Currently battling with excessive algae growth in your fish tank? Follow these steps below to prevent and control aquarium algae. I’ve used the below methods for combatting this unsightly substance to great success!

How to Prevent Algae

Preventing algae is far easier than eliminating it once it has developed and taken over your tank.

As mentioned earlier, a bit of it here and there is fine (and advantageous), but if left untreated, it can quickly overrun your aquarium. For reef tanks, having a gfo reactor and a carbon reactor using biopellets can help prevent algae growth.

Additionally, if you’re dealing with smear algae, spot algae, or other types that are hard to eradicate or potentially dangerous, you should take immediate action to remove it.

Reduce Lighting

Aquarium Led Light
Aquarium Led Light

Avoid placing your aquarium in an area that receives direct sunlight such as next to a window as this will contribute to algae growth.

Make sure you don’t leave your fish tank lights on for long periods of time – between 8 to 10 hours is sufficient for most freshwater aquariums.

In planted tanks that house plants with high lighting needs, around 12 hours is normally adequate.


Use a timer to turn your aquarium lights on and off each day if you’re unable to do it manually.

Control Nutrients

Excess algae is often caused by too many or an imbalance of nutrients in water, so you should work towards reducing these levels.

Test your tap water and aquarium for nitrates and phosphates.

To prevent and eliminate algae, nitrates should be under 10 ppm and phosphates should be under 0.5 ppm.

Avoid overfeeding fish food, overusing fertilizers for aquarium plants, and consider using phosphate removal aquarium products if your water contains too much phosphate.

Increase Water Changes

Frequent water changes are important for maintaining good water quality and controlling nutrients in your tank.

You should change 20 to 25% of your fish tank water every week. Not only will this improve the condition of your water, but it will also keep nitrate levels low – one of the causes for algae growth!

Keep Natural Algae Eaters

Adding algae-eating fish and invertebrates to your tank can prevent and reduce algae overgrowth, but make sure your tank is a big enough size before you add any new residents.

Some great algae-eating species include:

Amano shrimp will also help keep your tank clean by eating uneaten food that’s left from your other tank residents.

Here’s more info about these algae eaters…

Best Algae Eater for Planted Tanks?

Adding Live Plants

A planted tank filled with plant life will help keep algae numbers low as aquarium plants will absorb many of the same nutrients that algae utilizes. They also provide a more natural habitat for your fish.

Some of the best live plants to help control algae are java moss, amazon swords, vallisneria, dwarf sagittaria, and water lettuce as they are all fast-growing species, which means they will absorb a lot of nutrients in your water.

I personally use vallisneria as it’s easy to keep and makes your aquarium look like an underwater jungle!

Final Thoughts

I hope I helped you learn how to identify the types of algae and the best ways to remove them. Remember, reducing indirect and direct light, controlling nutrient levels, and frequent water changes are all effective for preventing this pesky gunk from building up in your tank.

Be sure to share this guide around with your friends and any other aquarists you know. Check out my other aquarium-related articles if you need more advice on all things fish!

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