How to Kill Black Algae in Your Swimming Pool

Have you ever heard about black algae? If not, it is important to know that these seaweeds are one of the hardest algae to get rid of. This type of algae has very deep roots which are growing into the side of concrete pools. Algae spores can always be present in your pool, but they are able to bloom when the right conditions are present. This species of algae can be the most difficult to treat, but there are various ways to clean your pool and get rid of them. However, prevention is always the best approach and you must be aggressive!

Understand These Species

Like any other species, these black plants are usually coming from the ocean and can grow quickly in warm water. They have a protective outer layer that makes regular sanitization ineffective, so it is important to understand that they are chlorine-resistant. They are not harmful, but their presence may lead to the presence of other bacteria in the swimming pool. Usually, algae tend to bloom in those pools with poor filtration, a high pH level, and a low chlorine level. Plus, as you already know, they come from the ocean, so a common way for the pool to be infected by these algae species is by a bathing suit that has been in the ocean. Therefore, if you want to prevent this problem, it is recommended to wash your bathing suits after swimming. In fact, you need to sanitize everything, from bathing suits and toys to floats and equipment. Make sure you use a washing machine and a dryer because this can kill black algae.

How to Identify Them

These species of plants are actually of a blue-green color. It forms in the crevices of the pool’s surface, mostly in the shady areas. Although it is more common in plaster or concrete finished pools, you can have this problem no matter the type of pool you have. To make sure that you are actually dealing with such problems and not any other form of algae, it is necessary for you to be aware of how to identify it. Fortunately, this is very simple, as the algae are easy to recognize due to the fact that it leaves a heavy slime layer behind. It might not affect the clarity of the water, but it does make black spots appear on the surface of the water, thus being simple to identify it.

Test the Water Chemistry in the Pool

Every pool owner must know that the chlorine level needs to be somewhere between 1.0 and 3.0 parts per million. Plus, the pH level should be between 7.4 and 7.6. and the right level of alkalinity must be between 80 and 120 parts per million. These three levels should be tested at least once a week and corrected as needed. Make sure you will also test the calcium hardness. The ideal level is between 180 and 220 parts per million and it should be tested monthly.

Shock the Pool as Often as You Can

Work aggressively and shock your pool once a week, in order to remove chloramines and raise chlorine levels quickly. There are a few products which can help you do this, such as calcium or lithium hypochlorite, granular chlorine, and potassium peroxymonosulfate. Keep in mind to add the shock at night and run your filter 24 hours a day until the black algae have been removed. Furthermore, one of the best preventive measures for algae is to keep the water in your pool moving. This process will make it difficult for algae to take hold and it will also ensure that sanitizing chemicals are distributed. Remember to clean the skimmer and strainer basket regularly. Furthermore, you need to clean your filter. As you already know, a clogged filter will slow down the flow of water. Therefore, in warmer months when algae will bloom, you need to run the pump for eight hours over the course of the day.

Use Preventative Algaecide

If you have had any trouble with algae in the past, it is recommended to use some algaecides. The metal-based (especially cooper) algaecides are necessary for fighting against this problem and they should be added to your pool on a monthly basis. However, if you still have problems with algae growth, ass preventive algaecide to the pool on a weekly basis. Cooper has ions that kill black algae. In fact, it naturally deters and inhibits growth. Nowadays, most pool suppliers come with a wide range of clarifiers and algaecides for swimming pools, but if you use them for the first time, it can be a little difficult to make the right choice. Some algaecides are used to treat the algae while others are used like preventative. If algae have grown in a swimming pool, the treatment with algaecide and shocking will help you get rid of this problem. Also, you should think more about brushing and vacuuming your pool on a weekly basis, because these actions will remove spores and prevent algae from taking hold. By using a steel or a nylon brush, you can clean the walls, floors, and steps of the pool.

Keep Brushing Your Pool

If you are an owner of a swimming pool and you want to destroy black algae, it is recommended to brush daily the algae-affected areas with a proper brush. The black algae have a protective layer that will make them impervious to regular sanitizers, so you need to brush them regularly to break through this layer. Black algae have deep roots and if the roots are not destroyed, the organism will continue to grow back. As such, by breaking through this layer, you will let the chlorine and algaecides act and kill the organism. Additionally, you can use an automatic pool cleaner. Before purchasing a pool robot, it is important to know that there are three different types of automatic robots, such as pressure side, suction and robot pool cleaner. Each model comes with advanced technologies and impressive features. Some of them connect to your skimmer and use the pool’s filter to move around, while others move around the pool on their own and scrub the floor, steps and walls. However, most of these models can scrub, vacuum and clean the pool’s surface, helping you get rid of black algae.

Frequently Asked Questions

1 What causes Algae problems?
According to several specialists, a lack of good circulation, filtration and sanitation is usually a contributing or the primary cause of pool algae.

2 Are Black Algae difficult to eradicate?
Black Algae are the most aggravating strain of algae and it can be extremely difficult to eradicate completely due to their strong roots and protective layers.

3 How is Black Algae prevented?
Proper chemical balance and sanitizer levels will prevent many opportunities for algae to bloom. High pH and low chlorine can give algae a great start.

4 Are the copper-based algaecides better than the polyquat algaecides?
Both types do a great job. They both prevent and treat algae growth. The difference between them is that the second option is a bit safer than the copper based algaecide.


  1. Jannet says:

    Will cleaning the pool regularly with an automatic pool robot help prevent the appearance of black algae?

    • Becky Eddinson says:

      Cleaning your pool on a weekly basis with a pool robot will help you remove spores and prevent algae from taking hold. Also, you can use a steel or a nylon brush to clean the walls, floors, and steps of the pool.

  2. Andrew says:

    Can I swim in the pool while it’s being treated for black algae?

    • Becky Eddinson says:

      It is not recommended to swim in a pool while it is being treated with various chemicals because they can be absorbed through your skin and can be extremely dangerous.

  3. Briggite says:

    How long after treatment with algaecide is it possible to swim in the pool?

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