Black algae are a common plague for swimming pools worldwide. Deceptively named, these organisms are actually cyanobacteria, capable of transforming a refreshing dip into an unpleasant experience. Originally hailing from natural bodies of water, they can easily find their way into a pool via a swimmer’s attire. Thriving in sunlight, these bacteria proliferate, misleadingly masquerading as molds on the pool’s surfaces.
The presence of black algae, also referred to as blue algae, is not just a matter of aesthetics. These cyanobacteria produce potent cyanotoxins, potentially leading to nausea, stomach cramps, and even liver damage if ingested. Their existence in a pool thus requires immediate attention, as they pose a significant health risk to both humans and pets.
This article aims to guide readers through seven comprehensive steps to rid their pools of this nuisance effectively.
- Vacuum the pool floor to remove any coarse dirt that could hinder the removal process.
- Employ a steel brush to scrub off the algae. This is necessary due to the algae’s complex shell and slime layer that make them resistant to chemical agents.
- Utilize an algaecide, specifically designed to combat algae, to inhibit their growth.
- Sprinkle chlorine granulate on the infested areas, particularly the pool floor. This is a crucial step to eradicate the algae completely.
- Perform a pool shock, a process of over-chlorinating, to eliminate any remaining black algae.
- Regularly monitor and maintain optimal water parameters to prevent future infestations.
- Seek professional help if the infestation persists or if there are indications of larger issues with the pool’s structure or circulation system.
While the occurrence of black algae in pools can be a daunting challenge, it is not insurmountable. The subsequent sections delve into a detailed explanation of these steps, offering a comprehensive guide to reclaiming the pool from the grip of these pesky invaders.
What Are Black Algae In Your Pool?
Black algae, contrary to its name, isn’t actually algae in your pool at all. It’s a type of bacteria known as cyanobacteria.
This sneaky little organism can hitch a ride into your pool on someone’s swimwear, especially if they’ve recently taken a dip in a natural body of water like a river or lake.
These use the light energy of the sun to produce various organic substances. In other words: no algae can survive without light.
Black algae (also known as blue algae) are neither plants nor algae. They are wrongly called algae but belong to the cyanobacteria group.
But how do the black algae develop in the pool?
How Do Black Algae Appear In Your Pool?
Black algae are introduced into the pool water either by humans or pollen count. First, this stubborn type of algae grows in the joints of the pool and then spreads further and further into the pool. Therefore, a pool in poor structural condition is an ideal nesting place for the black algae to multiply.
Black algae prefer neutral and slightly alkaline waters.
The bad thing is, black algae can be a bit of a chameleon. It often appears as black or blue-green spots or clumps with raised heads attached to your pool surfaces. If you see something that looks like mold forming on your pool surfaces, you may be dealing with black algae.
PVC pools or stainless steel pools have no joints and were welded – Black algae is rarely found in these pool forms.
You are not completely powerless if you have a problem with this type of algae in your pool.
I explain below in this article preventive measures against black algae in the pool.
Are Black Algae In Your Pool Harmful?
Black algae (blue algae) are considered dangerous and have no place in a pool. Since these types of black algae produce cyanotoxins (one of the strongest poisons), the following three symptoms of the disease can occur.
- Nausea
- Stomach cramps
- Liver damage
Symptoms usually occur when adults or children swallow pool water contaminated with black algae. But pets can also get sick if they drink water that contains black algae.
Avoid the pool and forbid its use as soon as you have discovered black algae! Swimming is only possible again when the black algae have been completely removed from the pool.
In the following chapter, I explain how you can take preventive measures against black algae in your swimming pool.
What Equipment Do You Need Against Black Algae?
Due to their nature, black algae are particularly resistant and cannot be eliminated with simple home remedies. That is why you will find a list with seven necessary products to combat black algae in your swimming pool.
- A pool brush with steel bristles (not for GRP and liner pools)
- Algaecides that are used specifically against algae
- Chlorine granulate or liquid chlorine for shock chlorination
- Chlorine tablets to permanently produce free chlorine
- Pool floater for the chlorine tablets
- Pool test strips for the water quality
- Safety glasses and plastic gloves
This pool equipment is sufficient to clean a pool infested with black algae.
Some advisors even recommend replacing the sand in the sand filter system beforehand. If your pool is heavily infested with black algae, it can’t do any harm to replace the filter sand in the sand filter system.
1. Vacuum The Pool Floor
First, you should completely vacuum the coarse dirt from the pool floor with a pool vacuum. The dirt and the fine suspended matter impair scrubbing with the steel brush and would only be whirled up.
In the worst case, when you brush, you will miss some places where the black algae are sticking. To prevent this from happening and keep the view clear, I may recommend a battery-powered pool vacuum.
You can skip this step if there is no heavy soiling from leaves or sand in the pool.
2. Use A Steel Brush
Chemical agents are not enough because black algae are difficult to remove without a suitable brush due to the slime layer and its complex shell.
Scrub the pool thoroughly, and a second time with the steel brush if necessary.
Small black spots on the floor or the walls can be removed with a targeted application of chlorine granulation.
Break a chlorine tablet and rub the black algae with the edge. Wear gloves or use a holder for the tablet. As soon as the algae turn brown, they have died and can be brushed off.
Tip: Do not use a steel brush in a liner or PVC pool. In this case, you use a normal pool brush and scrub longer.
3. Use An Algaecide
The algaecide is used to combat specifically algae in the pool and is available in three different qualities.
- Slightly foaming algicide
- Strong foaming algicide
- Non-foaming algicide
To inhibit a new growth of algae in your swimming pool, I recommend adding some algaecides to the pool water. You can improve the algaecides effect by increasing the chlorine value – I recommend adding approx 125 g of chlorine per 25 m³ of pool water. However, the pool algaecide is far from sufficient. It is only used – as already mentioned – to reduce the growth of black algae. The pool shock in the next step is crucial in the fight against black algae.
4. Sprinkle The Pool Floor With Chlorine Granulate
Suppose the bottom of the pool is mostly infested. In that case, you should sprinkle it completely with chlorine granulate – switch off the pool pump beforehand.
Do not aim at individual spots and scatter the soil over a large area. I recommend using chlorine granulates.
Suppose the black algae are predominantly on the walls. In that case, a targeted application is not possible. You have to scrub the algae with a steel brush before using the chlorine granulate – you can rub the algae with a chlorine tablet beforehand.
Keep brushing until all the black algae fall to the floor. Then it would be best to sprinkle the pool floor with chlorine granulation as described.
Wait for a windless moment when sprinkling and wear protective goggles and a protective mask. After sprinkling with chlorine granulate, let the pump rest for 24 hours to build a chlorine cushion.
After the 24 hours have elapsed, the black algae are sucked off with the filter system or a pool vacuum. A pool shock is needed to inhibit further growth and kill the last black algae, which I will explain in the next chapter.
5. Perform A Pool Shock
To kill any black algae, the pool has to be shocked, i.e., over-chlorinated. Non-stabilized liquid chlorine may be suitable for shock chlorination in the pool. The amount used depends on the concentration.
- With a chlorine level of 80 g/l, 10 liters of liquid chlorine are used per 25 m³ of water.
- With a chlorine level of 150 g/l, 5 liters of liquid chlorine per 25 m³ of water are sufficient.
I recommend this liquid chlorine that you can buy online.
Furthermore, the liquid chlorine, in combination with a dosing system, is wonderfully suitable for permanent disinfection of the pool.
You can avoid splashes during the pool shock by pouring the liquid chlorine into the flow of the return nozzles.
After the pool shock, the pump should run for 24 to 36 hours until the water is clear again.
Measure the chlorine content every day and keep it above 2 ppm.
The filtration can be increased by using a flocculant in your swimming pool.
During this time, scrub the basin with a brush to remove all algae.
You can only take a bath again when the chlorine values are below 1.5 ppm.
My tip: The liquid chlorine is irritating, and you should wear appropriate protective equipment here. If you don’t have protective equipment, at least wear sunglasses.
What Are Preventive Measures Against Black Algae In A Pool?
A short filtration time is one of the most common reasons for an algae problem. Furthermore, algae are always formed when disinfectants are not used properly. You can prevent algae simply by taking care of the pool.
The following 3 parameters should be observed when treating the pool water against black algae.
- pH: Between 7.2 and 7.6
- Alkalinity: The total alkalinity should be between 80 and 120 ppm
- Calcium hardness: A value of 200 to 400 ppm is optimal
An electronic water test helps you precisely determine all pool water parameters.
Suppose you notice that the pool water is slowly becoming cloudy or algae are forming. In that case, this indicates that the filtration is too short.
The solution: Scrub the swimming pool with a pool brush and let the pool pump run longer until the water clears again.
You don’t have to use any extra chlorine here, either.
In addition, you should brush the pool regularly so that the algae do not continue to grow.
This process also favors the effectiveness of disinfectants in combating black algae.
Copper sulfate may be suitable as an additional algae killer. However, this agent is based on heavy metals and is therefore considered questionable.
A far better alternative for the preventive measure against algae is silver.
Products containing silver for pool maintenance are safe for bathers and can be added directly to the water.
In addition, silver-containing care products are highly effective in combating algae.
What to do if the disinfectants don’t work?
It is difficult to determine that disinfectants are not working properly.
The consequences are often not announced in the pool, and the pool water suddenly tips over.
Only the shock chlorination described above can help.
Can Black Algae Damage Your Pool?
Black algae can cause staining on your pool surfaces, especially if it’s left untreated for a long time. Plus, the slippery patches it creates can make your pool unsafe to swim in.
Is Black Algae a Sign of a Bigger Problem In Your Pool?
Persistent black algae can sometimes be a sign of a bigger problem with your pool. It might indicate issues with your pool’s circulation system or chemical balance.
Professional pool maintenance is not the only way to prevent black algae. I described above that the black algae nestle in the joints of the pool. If you do not successfully kill the black algae in the pool with my described method, then only one thing will help. The water has to be drained completely, and the basin has to be renovated.
Therefore, you should not only clean the pool after the winter but also examine the pool for damage and cracks. If necessary, repair the cracks in the spring before filling your pool.
