­­Why Do Algae Grow in Your Fish Tank?

Having a pet fish is a great experience for most people.

The Ultimate Guide To Saltwater Fish…

Watching them swim around and taking care of them is a great hobby and it also helps to relieve stress. Also, having a fish tank in your home or office can help brighten up the place. The beauty of a fish tank cannot be compared to another and that is one of the reasons why most people get it.

But so every often, this beautiful fish tank becomes less attractive because of the growth of algae. They are seen as slimy growth on different surfaces on the tank and on the glass of the tank. This is one of the reasons why most people who are new to having a water tank quit almost immediately after they start. They wonder what caused it, or where it is coming from, or what they are not doing right. Sometimes it even becomes difficult for them to get rid of it.

The growth of algae in your fish tank, if moderate, can make it more beautiful and add a natural look to it. However, it may get out of hand when the growth becomes uncontrollable. When it gets to such a level, your fish tank will no longer be good looking and the algae can even grow on your fish or affect your fish.

In this article, you will learn everything about algae and why they grow in fish tanks. You will also learn if they are good or bad and what you should do if you find them growing in your tank.

What are Algae?

Algae are plant-like living organisms that are usually found in water or damp places. They make their own food through the process of photosynthesis in the presence of light. Algae are not classified as plants because they are usually microscopic meaning you cannot see them individually with your eyes.

The reason why they appear as visible in water is when a lot of them have come together. The green coloration they have is because of the pigment called chlorophyll which they use to trap the energy from sunlight. Chlorophyll is green.

However, there are few large species such as the common seaweed which are large enough to be visible. But they are still not regarded as true plants because they lack the basic organs in plants such as leaves and roots. Alga is the word for one of them while algae is plural for more than one.

Photosynthesis is the process by which all green plants make their own food in the presence of sunlight and carbon dioxide. This process takes place in the presence of water and carbon dioxide. This results in the production of sugar which is the main food of plants and the byproduct of this reaction is Oxygen.

Since algae are the most abundant green photosynthetic organism, they actually contribute more oxygen to the atmosphere than oxygen produced from any other source.

Since algae thrive in the presence of water, they are found in most water bodies from the oceans, rivers, lakes, streams, and any other water body you can think of.

Algae are also found in fish tanks and that will be the main focus for this article. Let’s take a look at some of the common types of algae which you will likely find in a fish tank.

The first and most common type of algae in fish tanks is green algae. As you can guess already, they appear greenish because of the presence of the green pigments which they use to trap energy from light sources. They serve as natural food for some grazing fish and they can be found growing on the surface of fish tank rock and other apparatus in the tank. They are usually difficult to get rid of as they grow on more surfaces.

The next algae that are important to fish tanks is red algae as well as brown algae. The pigment found in this algae which they use to trap energy from sunlight is red. Hence, when they come together they appear to be reddish. They usually appear like brown dust that covers the surface of almost everything in the tank and the walls of the tank.

They are caused by high-level phosphate in the water. They are easy to get rid of if you have other live plants in the water. They will absorb the phosphate thereby leaving them with no nutrients. They will die off and algae-eating organisms can take care of the remaining.

Another type of algae growth you may likely experience in your fish tank is the one that causes “green water”. This is a situation caused by microscopic algae suspended in the water. You cannot get rid of them by cleaning the wall of the fish tank or getting algae eating fish inside the tank. They are usually caused by excess nutrients which leads to their bloom.

They can be removed by first eliminating all the sources of exposure to the direct light.

The next step is to do a complete water change up to 30% to reduce their population. However, this will only reduce the population for a while.

The best thing to do is to find out where the excess nutrients are coming from. Most of the time it is from the fish feed which is high in protein. Reduce your feeding rate and change water frequently until you achieve a balance in your fish tank.

Why do Algae Grow in Your Fish Tank?

This is the question that most new fish hobbyists usually ask. They want to know why algae grow in their fish tank. They wonder if it is something that they are not doing right that is making these algae grow.

Well, it may be as a result of something you are not doing right but that is not usually the case. Algae are everywhere so the growth of algae in a fish tank is a natural occurrence. There are algae in the natural habitat of the fish so it should not be strange to you if you find them growing in your fish tank.

So where do all the algae come from?

As I said, algae are everywhere and they reproduce mainly through spores which is similar to seeds in land plants. The spores are everywhere in the air, water and they are transferred by some living organisms which act as carriers. And they only need a suitable condition to grow.

What are the Things that Influence the Growth of Algae?

There are two major factors responsible for the growth of algae in a fish tank and they are the presence of light and nutrients.

Light is needed for photosynthesis to take place while nutrients are needed for growth. The two main limiting nutrients for the growth of algae are nitrogen and phosphate. They are called limiting nutrients because the absence of them will limit the growth of these algae. Once these two nutrients are available, algae find the fish tank suitable for growth and begin to multiply rapidly.

The common source of this nutrient in the water is from the fish feed. Fish feeds are highly nutritious and when they decompose in the water, they release these nutrients. The algae take it up and use it for growth. The common source of nitrogen is from nitrogenous substances in the water such as ammonia and nitrates. Ammonia and nitrates are usually abundant in the water because fish excrete their waste as ammonia. “

The other factor responsible for the growth of algae is the presence of light. If you have your fish tank by the window you need to change the location. Natural sunlight is the best way to let algae grow very fast. You may consider changing the location of the fish tank or adding background wallpaper that will prevent the direct penetration of light into the tank.

Direct sunlight can also increase the temperature of the water and that of the fish thereby increasing their metabolism and stressing them. So don’t think you are doing the fish a favor by placing the fish tank directly under the ray of sunlight.

“The LED light in the fish tank can also cause the growth of algae. It is best to put out the light when you are not there. When you go to sleep turn it off. You are the one who needs it to see the fish, the fish don’t really need it. So don’t hurt the fish by letting the light stay on forever and encourage the growth of algae.

We all love to see our fish happy so we want to feed them until they are satisfied. This seems like a good thing to do but it will actually encourage the growth of algae. Fish don’t often eat all the food you put inside the water for them although you see them always coming up as if they want more.

The uneaten feed will accumulate and later decompose thereby leading to the release of nutrients that the algae need to grow. When you overfeed your fish they will also produce more quantity of waste too. Since their primary waste is a rich source of nitrogen it becomes a source of the problem and provides nutrients for the algae to thrive on.

The presence of a live plant in a fish tank will help you control the algae growth. Since they need the same or almost the same condition to grow, the presence of live plants may inhibit the growth of algae by competing with the same resources that they need to grow. Healthy plants will be able to take up nutrients faster than the algae and hence leave the algae to struggle and limit their growth.

How to Prevent Algae from Growing in Your Tank

The easiest way to control algae in your fish tank is to prevent their growth. This starts with the management practices you employ in taking care of your fish tank. Although it will be difficult to totally prevent the growth of algae, you can maintain a population that will not be harmful to the fish.

This can be achieved by maintaining good water quality. Always make sure to change at least 30% – 50% of the water in your tank weekly. Good water quality is healthy for your fish and limits the growth of algae. Once in a while, you need to clean the glass and vacuum the substrate to get all the accumulated particles off the tank.

How to get Rid of Algae in Your Fish Tank

Having a little growth of algae in your fish tank gives it a nice look. It makes it look as if it is their natural home which adds to the beauty of the tank. However, waking up one day to find out that the algae have taken over your tank (which is possible) is the last thing that you want to happen. When you start noticing the growth of algae, it may be a sign that they are becoming excess and you need to get rid of them.

The growth of this algae may become undesirable as they increase and you have to do something about it. They can make the fish tank become unattractive and also affect the fish. It is impossible to get rid of the algae completely by removing them. Instead, you must find the root cause and eliminate it.

So What do You do When Algae Have Started Growing in Your Tank? “

When you begin to notice the growth of algae in your thank the first thing you should do is to look for the cause. Think of what you have done differently in recent times. Did you leave your fish for someone else to feed? Did they overfeed the fish? Has it been long that you last changed the water in your tank?

These questions will give you a clue about what you should do to achieve the maximum results. Don’t look for chemicals to get rid of the algae in your tank because there are natural means of getting rid of them and they are effective.

Since they have the same requirements to grow as plant it is important to consider this fact while trying to get rid of them. If there is any general action you apply to the tank it may not only affect the algae but it will also affect your live plants in the fish tank. Below are some of the methods that you can use.

Introduce Algae Eaters into the Fish Tank

There are animals whose natural food is algae and they are called algivores. They are usually bottom feeders and make an excellent candidate for fish tanks that are prone to algae growth. They include some species of fish, shrimp, and snails.

You should know that these algae eaters are effective but the effectiveness depends on the level at which the algae has grown. If the growth has become extreme they may not be able to do much. It is not a sign that they are not eating enough or avoiding the algae. There are more effective in a tank with minimal algae growth where they can easily control it and prevent it from getting much.

Fish Algae Eaters
Many catfish belonging to the family of loricariid native to South America are good at grazing algae. The three major genera that fall into this category are Otocinclus, Ancistrus, and Plecostomus.

Plecostomus can grow bigger and no longer suitable for the fish tank. They are also known to attack the live plants in the fish tank.

Otocinclus are great at keeping the algae at check. They have a small size and they prefer to be kept as a school. That is, you need to keep more than one of them, they should be kept in a school. That is about 6 of them together in a tank. Their effect can be easily seen since they are usually more than one.

Another fish that is good for controlling the growth of algae is the Siamese algae eater. They can live with other fish in peace and also eat almost anything that is available. They are also one of the few fish that will feed on the “black brush algae”.

The American-flag fish will also feed on the same algae and also a variety of other algae. They can however bully smaller fish that are in the tank.

The Chinese algae eater is the most common of 3 Gyrinocheilus genera. They are small in size and can easily live with other fish. But as they grow older, they become territorial.

The Butterfly Goodeid makes good algae eating fish for a fish tank. They are attractive and they also feed on the carpet-like layers associated with green hair algae effectively. This fish can however become aggressive in the midst of other species of fish.

Shrimp Algae Eaters

The Cherry Shrimp is small in size but the effect they have is not a small one. They feed on algae alone which means they are not going to destroy the live plant in the tank. They are sensitive to pH fluctuations and it is better to get more of them to deal with stubborn algae. There are several other examples of shrimps that are effective algae eaters. Some of them include the red rhinoceros shrimp, bee shrimp, Amano Shrimp, and the grass shrimp.

Snail Algae Eaters

Snails also make excellent candidates for grazing algae in a fish tank. Most of the freshwater snails will feed on algae if introduced into a fish tank.The problem, however, with snail is that they are likely going to attack your live plants in the fish tank.

Avoid Overfeeding

As a rule of thumb, never feed your fish with more food than they can consume in 2-3 minutes. If it will take them more than 3 minutes to finish the quantity of food you want to give them then you must reduce it.

First, their food is expensive and you shouldn’t waste it.

Secondly, it is stressful to get uneaten feed out of the water. You have to use a siphoning hose to get them out which can be tiring. When it decays, it produces a good ground for algae to grow. When you feed your fish too much they also produce more waste which is not good for the tank. It can lead to an ammonia spike which is dangerous to fish and makes algae grow faster.

Avoid too much Exposure to Light

Avoid placing the fish tank directly where sunlight rays can penetrate. Sunlight will provide the energy needed for photosynthesis and make them grow faster. Removing the fish tank from the light can help control the growth of algae.

Physically Remove the Algae from your Fish Tank.

This will require that your roll up your sleeves and get to work to remove the algae from your tank. You can do this by reducing the volume of water and scrape the walls of the fish tank.”

Effect of Algae on the Fish

Excessive algae growth in a fish tank can have negative effects on the fish.

First, it can reduce the oxygen level in the fish tank thereby lowering the amount of oxygen available for the fish. Green plants naturally produce oxygen but that is during photosynthesis during the day. At night, in the absence of light, they are not producing oxygen but rather making use of oxygen for respiration. They make use of the oxygen that is available for fish thereby reducing it for fish and exposing them to the risk of dying through lack of oxygen.

When algae die they begin to decompose. If you do not do anything to the dead algae in your fish tank it can have a devastating effect. This can also deplete the amount of oxygen available for fish in the water. When they die, decomposition takes place by bacteria called decomposers which make use of oxygen to carry out this activity. And since they will be using a lot of it, it can affect fish life and even kill them.


You have to understand that no matter how well you try you cannot get rid of algae 100%. Understanding how to keep them at a moderate level is the key. It is better to prevent their growth than to control it. It is always cheaper and easier that way.

Just do your best to maintain a good population that makes it look natural and remember if you have plant-eating fish it is a natural food for them. Algae cannot be removed completely. And remember that if you want to reduce the population, it is always best to look for the cause of the algae growth rather than treating the symptoms.

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