Aquarium algae: causes and solutions

As an aquarium owner, I take pleasure in watching my fish eloquently swim around the tank enjoying the plants around them. In the early days of my fish keeping journey; having placed a light in my tank, to enhance the overall spectacle; I noticed the water starting to change color. The glass developed some form of plant overgrowth. After some inquiries, I discovered that my aquarium was experiencing a type of algae overgrowth. While researching for the solution, I not only learned how to combat this but found this to be a common issue many aquarists face in their fish keeping journey; so no need to panic!

What exactly is algae?

Algae refer to a wide range of aquatic organisms that have the ability to photosynthesis. Photosynthesis is the process of harvesting light energy from the sun while generating carbohydrates. In addition to its photosynthetic role, it also plays a significant part in the food base for all kinds of aquatic life. 

Examples of the most common types of algae are seaweeds such as kelp, phytoplankton, pond scum, and algal bloom. The different organisms that fall in the category of algae are not all directly or closely related. However, they all have certain features that bring them together and differentiate them from other plants that can also photosynthesis, like land plants. Algae feature different types of life cycles and come in a variety of sizes. Micromonas are the smallest of the species, and kelp, the largest.

Common causes of algae overgrowth 

One of the most common causes of the overgrowth of algae in aquariums is excess light. The reason why is because algae survive by photosynthesizing light. Most, if not all, aquariums feature a light element that assists in maintaining the health of all the organisms that are present in the tank. The combination of unnatural light (from the light feature) plus direct sunlight tends to attract the initial growth of algae. 

Excess waste in a fish tank is another common cause for the development and overgrowth of algae, which happens when an aquarium hosts too many fish. The fish have to be fed and naturally, they also excrete. When there is too much leftover food inside the tank, it acts as a nutrient for the algae. 

Algae will also develop as a result of the nitrogen cycle in the aquarium. This happens in cases where there aren’t enough beneficial bacteria in the water to transform the ammonia from the nitrogen cycle into nitrates.

How to avoid it  

Below are some steps you can take to get rid of algae in your fish tank. 

Reduce lighting

As mentioned, a common culprit that causes algae to overgrow is excess light in the tank. It helps foster and quicken the process of photosynthesis resulting in the growth of the organisms. You can prevent this from happening by reducing the amount of light in the tank. If your tank is built with a lighting component such as an LED lighting feature, you can either find a smaller fixture or reduce the amount of light the bulb produces. Alternatively, you can keep your tank away from direct sunlight. 

Feed less

Excess waste from leftover food is a common cause of the overgrowth of  algae. The food leftovers provide the necessary nutrients that aid the growth. You can prevent this by feeding the fish the right amount of food, ensuring they eat it all, avoiding the build-up of any waste in the tank.

Water changes

Regularly changing the water in your aquarium will significantly help to reduce the chances of having an overgrowth. By changing the water, you prevent the tank from harboring wastes that act as nutrients for the algae. How regularly you change the water in the tank will depend on the amount of fish you are keeping and the size of the aquarium. 

Keep live plants

Keeping live plants will help prevent algae from overgrowing. This is because they compete for the nutrients and light that would otherwise be used by the algae.

Be quick to clean Up

A dirty tank packed with waste is far more likely to suffer from an algae overgrowth. Cleaning the tank will get rid of the waste that would otherwise become nutrients for the organisms. It will also help remove the small amounts of algae, therefore, not giving it a chance to overgrow in the first place. 

Consider keeping algae eating fish

Algae eating fish do what they say on the tin. By eating the algae, they prevent the organisms from thriving to the level that causes the overgrowth. 

5 Common types of aquarium algae

  1. Brown Algae
  2. Blue-green Algae
  3. Red or Beard Algae
  4. Hair Algae
  5. Green Water Algae

1.) Brown Algae:

Brown algae will appear as a slimy film on the glass, substrate, and plants in the aquarium. It tends to grow very fast and is prevalent in freshwater tanks. The organisms thrive during the nitrogen cycle. What starts as brown patches on the gravel and the glass of the aquarium will proceed to become a full-blown issue within less than five days if not taken care of immediately.

What are the common causes?

  • High amounts of phosphorous, silicates and nitrates
  • Too much or too little lighting levels in the tank
  • Low amounts of oxygen in the tank
  • Silica that has built up – usually from tap water and  types of substrate 

How do I remove it?

Brown algae are easy to remove since it doesn’t adhere to the surfaces of the tank. Therefore there is no need to scrub the surfaces when removing it. Start by wiping all the surfaces and vacuuming the gravel. You can also use water changes to remove and dilute the nutrients that the algae feeds on. Adjusting the lighting in the tank will also help the process. Finally, introduce silicate absorbing resin in the filters, fish that feed on this type of algae is also advised.

How do I prevent it?  

  • Adjusting the light levels in the tank
  • Acquiring algae eating fish
  • Constant water changes

2.) Blue-green Algae:

Scientifically speaking, green algae is not an alga. Instead, it is a cyanobacterium, also referred to as smear algae or slime. It tends to increase and cover everything that is in its path, including the substrates within the tank. Sometimes it gathers as a foam-like scum on the surface of the water. A slim physique characterizes this type of algae as well as giving off a very unpleasant fishy stench. It can be a variety of colors from Blue, brown, green or even a reddish-purple. Like other types of algae, this alga is capable of photosynthesizing, and acts as a nitrogen-fixing bacterium, which isn’t good news. 

What are the common causes?

  • Excess light 
  • Excess waste from the overfeeding of the fish
  • Failure to change the water in the aquarium as often as needed.

How do I remove it?

Unlike brown algae, removing this type of algae from the tank is not as easy. You will have to scrub it thoroughly from the surfaces of the tank. You can also use chemical products that contain erythromycin, which will help to remove and ease the process. 

How do I prevent it?  

  • Reduce the light in the tank.
  • Regularly changing the water in the tank.
  • Using erythromycin.

*Note that blue-green algae cannot be prevented by keeping algae eating fish since there isn’t a type of fish that eats this particular organism. Therefore, to prevent overgrowth, you can only use the measures mentioned above.

3.) Red or Beard Algae:

Beard Algae belongs to the red algae family, which tends to grow on the edges of the plant leaves and any hard surface. When it grows, it forms dense patches that resemble a dirty green beard, hence the name. At times, it’s bright green, blue-green, or black. It’s characterized by its speedy growth and being soft and slippery. It will cling very hard to surfaces making it challenging to remove. 

What are the common causes?

One of the leading causes of this type of algae is unstable or very low levels of carbon dioxide in the aquarium. When the level of carbon dioxide is low, the plants are unable to utilize the fertilizers and the light available to undergo photosynthesis.

How do I remove it?

Because it clings to the glass of an aquarium, it’s not that straightforward to remove. It can, however, be removed by introducing fish that will eat it. Examples of fish that eat this kind of algae are Florida flag fish and the  Siamese algae eater. Adding additional carbon dioxide to the tank can also help remove the algae as well as certain bleach solutions. 

How do I prevent it?  

  • Rearing fish that feed on beard algae
  • Getting rid of contaminated plants
  • Regularly cleaning the tank and changing the water
  • Restoring the level of carbon dioxide in the tank

4.) Hair Algae: 

Hair Algae actually referring to the many types of algae that look like wet hair. Common ones you may have heard of are green hair algae, string algae and thread algae. They are a nuisance because of their speedy growth rate, and will usually occur on the back of either too much nutrient or not enough; usually belonging to the genus, Oedogonium.

It’s characterized by long green threads that will form a slimy carpet like layer over the  plants and decorations. 

What are the common causes?

  • Mostly occurs in new aquariums that are going through the cycling phase. This is because beneficial bacteria has yet to occur inside the aquarium.
  • Changes in the chemistry of the water (in particularly C02 levels), technical equipment, and the mass of plants within the aquarium. 

How do I remove it?

Getting rid of hair algae can be a real nuisance and will take some time. An obvious way to remove it is to manually rip it from the rocks and plants, which will do half the job. Carrying out regular water changes is also recommended as well as lowering the light intensity towards your tank. Hydrogen peroxide can also be used. However, it’s important to know that this is a highly corrosive powerful product that needs to be handled with care. 

How do I prevent it?  

  • Frequent water changes 
  • Regular cleaning 
  • Keeping algae eating fish in the tank
  • Using hydrogen peroxide inside the tank water

5.) Green Water Algae:

Green water algae, also known as green aquarium algae, is one of the most common freshwater aquarium algae around. While it may look unattractive, it does not have any adverse impact on the fish inside the tank. Its occurrence will turn the aquarium water opaque green. Sometimes overrunning the entire tank, obscuring its transparency.

This type of algae grows by photosynthesizing light. It’s a unicellular organism, and its rate of growth is speedy.

What are the common causes? 

  • Excess light inside the tank, especially exposure to direct sunlight.
  • Excess of nutrients from left over food  and fish waste

How do I remove it?

One of the easiest ways to remove the algae is by carrying out frequent water changes. However, this will not prevent future occurrences; cleaning the tank is also recommended. You can also introduce fish that feed on this specific type of algae-like daphnia.

How do I prevent it?  

Note that removing the algae from the tank does not mean that it won’t occur again. In fact, in some cases, it leaves room for a new breed to occur. Therefore, the following measures should be taken to prevent another bloom after removal.

  • If your tank is exposed to excess sunlight, the first prevention measure should be to cut off the excess light. 
  • Introducing fish that feed on this specific type of algae.
  • Regularly cleaning the tank.
  • Avoid hosting too many fish in the tank.
  • Don’t overfeed the fish.


Different types of algae can infest your aquarium depending on the unique conditions your aquarium holds. Therefore, the only way to come up with a solution is to first understand what type of algae is present in your tank. I hope the above has been helpful, and if you have any burning questions as always, please don’t hesitate to contact us. 

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