Beginner's Guide

Algae in Fish Tank: Type, Cause and Control

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Algae are unicellular or multicellular organisms that have no root, stems, and leaves but do have chlorophyll, and you can mostly find them in water. Algae in Fish Tank play a very complicated part in the ecosystem, i.e., they can act as food to aquatic life, and some species of them intoxicate the water that they reside in. 

A fish tank without any algae is a myth. Your aquarium can be free of the algae overgrowths, but they reside in a microscopic unicellular form that cannot be visible via our naked eyes. They are present in the biofilm, along with many other microorganisms and bacteria. In this article, you will get to know about the cause of algae overgrowth, how to avoid it, and brief knowledge on its various types.      

Is Algae That Bad For Your Fish

The answer to this question can get tricky because algae can be both good and bad for your fish at the same time. Algae can act as a secondary food source for your fish. Like any other plant, it produces oxygen, which is good for respiration. It can also act as filtrate to filter out ammonia, nitrite, and phosphates. In simple words, it contributes to the nitrogen cycle.

 But when you already have a working filter, you provide food to your fish regularly, then why do you need algae? You don’t need algae in your fish tank. Its good sides are all secondary, whereas the bad sides can critically affect the tank’s ecosystem. Excessive unwanted algae can deprive you of having a beautiful aquarium that you have always dreamt of. Algae, in massive amounts, can absorb all the dissolved minerals in water that could have been beneficial to your fishes.  

What Causes Excessive Algae

There are several reasons why your fish tank has excessive algae than it should have. Some common reasons are:

  • You left your lights on for too long.
  • You have placed your aquarium in such a location that it gets direct sunlight most of the day.
  • Your water has become highly nutritious due to the leftover food and fish wastes. This nutritious water is a hospitable environment for algae to grow.
  • You are providing so much food to your fish that they probably aren’t noticing the algae growing around them, which is safe to consume.
  • The absence of algae-eating herbivores in your fish tank is also a reason. If there are carnivores only present in your tank, then the overgrowth is certain.
  • You don’t perform water change regularly. The algae are the bioindicators for a water change.  

Types Of Algae

You can divide algae into different types based on the water conditions and their appearance. They are:

Black Beard Algae (BBA)

These algae grow in both fresh and saltwater and produce a protein called phycoerythrin that contributes to its purple-black appearance. Black Beard Algae can often be seen on leaf edges of slowly growing plants and sometimes attached to a metal surface. It grows as a crowd of tufts and can be seen as long as 0.5 cm. Black Bread Algae is mainly caused due to the fluctuation of carbon dioxide levels in the tank. Imbalanced lighting can also contribute to its growth.

Blue-Green Algae (BGA)

Blue-green algae are not even real algae. They are aquatic bacteria called cyanobacteria that are able to photosynthesize. You can find them as a blue or green slimy mat structure. It can be easily peeled off but can grow back quickly at the surface or substrate where it receives light. Poor water circulation is its major cause. Dirty substrate and filter medium can also make it grow. 

Cladopora or Blanket Weed

Cleadopora or Blanket Weed is a branching, green algae with threads like structure. It feels rough when you touch it. The blanket weed is caused due to low CO2 and low nutrient levels. To remove it, you must gradually increase the carbon dioxide level and remove it manually. You must also ensure that water circulation is good. 

Brown Algae or Diatoms

These algae can be seen in a newly setup aquarium because they obtain nutrients via chemicals like nitrates and phosphorus. You can see them as brown patches on the surface, substrate, and glass. You can find these algae in both fresh and saltwater. We can see them in tanks where 100% tap water and used, and where you can find nitrates and phosphates abundantly. These algae can be vacuumed or scratched out and will completely disappear from a new tank when the filter and substrate have matured.

Green Dust Algae

They are formed on the glass as dusty structures all over the tank. Sometimes they are so dense that you will not be able to see through the glass. They are quite common on newly setup tanks and grow due to low nutrients and low carbon dioxide levels. If you do not cycle your tank properly, then they can grow. The best way to get rid of it is by letting it complete its lifecycle of about four weeks and die off.

 Green Spot Algae

They are often mistaken for green dust algae, but unlike them, these algae occur as green spots on the walls of your tank. Sometimes these spots can be seen on slowly growing leaves. Poor water conditions, too much lighting, low level of phosphates, and low carbon dioxide can contribute to the formation of green spot algae. Increasing the phosphate and carbon dioxide levels can help you get rid of these algae.

Green Water / Algae Bloom

Water turns cloudy green due to the presence of unicellular algae that can multiply rapidly. These algae can turn your tank water completely green like pea soup. Ammonia spike is the main reason for the overgrowth of these algae. Imbalance in nutrients and too much lighting can also cause these algae to overgrow. A few days of blackout and a large water change can help these algae to die off.

 Hair or Thread Algae

This hair or thread-like algae are seen anchoring to aquatic plants and can vary in length. They are soft to touch and are loosely attached to plants. Lack of carbon dioxide is the main reason why they grow. You should minimize the lights, and you must increase the level of carbon dioxide to remove these algae.

Rhizoclonium Algae

These algae are similar to hair algae but have a slight slimy touch in them. They are very soft and can be formed in bushy forms. Weak water flow, lack of nutrients, and carbon dioxide can help them grow. Placing fish like shrimps will eat these algae. A good tank cleaning can easily reduce them.

Staghorn Algae

As their name indicates, these algae resemble the stag’s horn. They are grey in color and can be found in aquarium plants, décor, and equipment. Overfeeding your fish can create mulm inside the tank, and it acts as a foundation for these algae. Increasing carbon dioxide levels and using a powerful filter can reduce these algae.  

How to Avoid Excessive Algae

Reducing the Temperature

Algae loathe cold water. So, you can see algae in your tank mostly during the cold season when the water heater is running all day long. During the winter, it is almost impossible to find algae, but during summer, if you reduce the excessive use of heater and keep the water equivalent to the room temperature or below it, then you may not see any algae. 

Cleaning Tank Frequently

If you do not clean your tank regularly, protein and other nutrients build up excessively in the water. This excessive nutrient level helps algae to overgrow. So, try cleaning your tank regularly and thoroughly and perform frequent water changes.

Using Good Filter Media

Having excessive carbon and phosphate level in your tank can be advantageous for algae. So, by using filter media that filters out phosphate and carbon dioxide can be a good way to prevent algae overgrowth.  

Minimize Additives

Various additives in the form of food and chemicals are regularly added to the tank for various reasons. However, the overabundance of these additives should be minimized because they are all that algae need to feed on. 

Addition of Live Plants

Adding live plants in your aquarium increases the competition for nutrients and carbon dioxide. If you add more plants, then algae will not be able to receive the necessary nutrients to grow as the plants will outshine them. 

Frequent Water Change

You must always be aware of the chemical and nutrient content in your water. For this, you must perform frequent water changes. If the water has high phosphate content, then phosphate reducing chemicals must be added. You must always make sure that your tank is inhospitable for algae. 

Performing weekly water changes is the most effective way to avoid algae. This reduces the nutrients level in your water and removes the nitrate that is major fertilizers for algae. 

Cover Tank With Lid

If you aren’t using a lid for your tank, then it is certain that the water will evaporate off. So, while replenishing the water, you must always use dechlorinated water and phosphate reducing chemicals. 

Don’t Overfeed Fish

Feeding more than your fish requires can increase the phosphate level in your water. So, feed your fish in small portions, and if any food is left uneaten within 5 minutes, then remove it. 

Don’t Over Exposure Aquarium to Lights

You should use aquarium lights to about 8-10 hours a day. Unnecessary exposure to light will help algae grow. 

Do not place the aquarium under direct sunlight at any cost. This can be the major factor why algae are all over your tank.  

Clean Decorations and Gravels

Along with water and filter mediums, you must clean the decorations properly, and you must siphon the gravel. Leftover food and fish waste are sometimes stuck between gravels and somewhere on the decors where your filter can’t reach. So, checking on the decors regularly for and waste must be done. Using the siphon is the best way to clean the gravels.

Keep Algae Eating Fish

Algae eating fish like Chinese algae eaters, siamese algae eater, black mollies, etc. are very efficient in fighting off algae because some of them choose algae over fish food as their primary food source.  

How To Reduce Accessive Algae

If you already have too many algae in your tank, then you can reduce it in various ways. You can perform a complete blackout action on the tank. You can also stop feeding your fish for a few days so that they have no choice left than to eat algae. 

Equipment you will require to fight algae

Magnetic Scrapers


Magnetic algae scrapers are used widely to remove algae that are formed on the inside of your glass.

Razor Blade

Razor Blade

You can use Razor Blade for the stubborn algae that sometimes cannot be cleaned by scrapers. But while handling razors, you must always be careful that you don’t hurt yourself and the fish or don’t leave scratch marks on the glass. 



You can use bleach to remove algae from filter parts like pipes and outlets. But be sure that you are using it only on plastic materials. Anything that is made up of stuff like concrete or wood shouldn’t be bleached because they can absorb the bleach. While cleaning the filter parts, you must create a solution of 9 parts water and one parts bleach and immerse the algae affected device into the solution completely for a few hours. 

Algae Eating Fish For Algae Control

Various aquatic algae eaters can be kept in your tank for the reduction of algae. You can use shrimps, snails, and algae-eating fish to get rid of the algae from the ecosystem. Some of the popular algae eating fish that you can include in your tank right away are:

Chinese Algae Eater

  • Chinese algae eater: You can find this algae eater in any pet stores, and they can grow up to a relatively large size of 10 inches. They grow more aggressive as they get bigger, so they do well with cichlids. However, they are not the best algae eaters as they become lazier as they get bigger. But while they are young and small, they can eat various types of algae.
    Siamese Algae Eater
  • Siamese algae eaters: They are the most effective algae eating fish because they also eat the algae that others ignore like black beard algae. They are non-aggressive and peaceful hence easy to take care of.
    Sailfin mollies
  • Mollies: These fish, including other livebearers like platies and swordtail, are not that much of an algae eater, but they feed on it from time to time. They can reproduce quickly, so make sure that there is enough space for the fish. However, they do not prefer algae primarily, so you must give them regular fish food too.  

You don’t need to freak out whenever you spot algae in your tank because not all of them are dangerous. Some of them indicate that there is a good level of phosphate, nitrate, and nutrients present in the tank. They just remind you that your water needs to be changed. Some algae act as a secondary food source for your fish. So, having some algae in your tank isn’t that bad at all, but you should react quickly to it if they overgrow.


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