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4 Causes of Algae in Your Swimming Pool (And What to Do About It)

4 Causes of Algae in Your Swimming Pool (And What to Do About It)

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Enjoying a quick, refreshing dip in the pool is one of the greatest ways to spend your summer outdoors.

However, nothing is more off-putting than finding slimy algae lurking around and creating a murky mess in the pool.

Collecting and removing algae from the pool is fairly easy, but it will only take a few days for the green bits to show up again.

This is because you need to nip the problem in the bud so that it doesn’t come back again, and that’s where this guide comes in handy!

In today’s article, I’ll walk you through the most common causes of algae in swimming pools and how to deal with them the right way so they never come back.

How Algae Infect Your Swimming Pool

If you want to get rid of algae, you need to properly understand what they are and how they infect your pool.

Algae is basically a diverse group of aquatic organisms capable of producing oxygen through photosynthesis.

Unlike regular plants, algae lack true roots, leaves, or any kind of stems. In other words, they don’t have a developed vascular system to transfer nutrients through their bodies.

But similar to plants, algae primarily make use of light energy to generate their own nutrition and are also able to produce oxygen and other carbohydrates.

The defining feature of algae is that many of them are unicellular, and usually show up in many different sizes or forms. 

The most noticeable sign that there’s algae in your pool is water discoloration. 

Depending on the kind of algae that is infecting your pool, the color might vary. It could be either blue-black, yellow or even green.

Why Do Algae Spread Quickly?

The main reason algae spread so quickly is because they reproduce through their own spores. These spores then spread into different areas, and wherever they find a suitable spot to thrive, they will start to germinate and create new algae.

If you have seen algae growing in ponds or on the corners of lakes before, you probably noticed that algae need a certain set of conditions to grow.

For starters, the water needs to be stagnant. The water also needs to be within a suitable pH level, but more about that later.

Are Algae Harmful?

Pool-infesting algae aren’t harmful to swimmers. However, they’re quite slimy and smelly, which creates a disgusting environment that you don’t want in your pool.

Additionally, even if they’re not harmful on their own, the bacteria and pests that feed on them can be quite bad for your health, causing conditions like eye infections, rash, fever, and diarrhea.

Besides health problems, algae can harm your pool in several other ways. For example, if you have algae in your pool and you turn on the filters, it’ll end up clogging the filter.

Unfortunately, this can damage the filter beyond repair, so you might need to replace the filter altogether, which can be quite pricey.

Instead, you’ll need to manually remove the algae before turning on the filters. Needless to say, clearing out your pool requires additional time, effort, and money.

In conclusion, pool algae can harm you in a variety of ways, whether it’s through the gross effect, indirect health problems, or by damaging your pricey pool filters.

Now that you know what algae is and just how harmful it can be, let’s talk about the major causes of algae in a swimming pool.

Causes of Algae in a Swimming Pool

One thing you should know here is that algae exist in a huge variety of types and can find their way into your pool through spores spreading with wind. Additionally, they can also be introduced into the pool by swimwear that hasn’t been properly cleaned.

The most common one that infests pools is Cyanobacteria algae. These have a characteristic blue and green color and exist naturally almost everywhere, so they start to multiply when the conditions are right.

To put it simply, algae spores will always find their way into your pool and will start to bloom when the conditions are right. Here’s a quick look at these factors, and what you can do to avoid them.

1 – Poor Water Circulation

Ph Balance Can Help Decrease Algae

One of the main reasons why algae growth occurs in swimming pools is because of poor water circulation. 

Algae still need water to grow, so as long as the water continues to flow, you won’t have much to worry about.

You might not have realized it while swimming, but water continues to circulate throughout the pool consistently, moving from the pool into the filter and then back out again.

However, if the filter doesn’t work properly, water circulation will slow down, promoting algae growth.

Also, if you use a small filter for a large pool, dead spots will start to form in the pool, which are areas with significantly low water flow, and therefore, a much higher chance for algae to develop.

To avoid this problem, you’ll need to carry out regular testing to determine whether the water is flowing consistently in all areas of the pool or if there are spots where the flow is considerably reduced, or if a dead spot exists.

Some homeowners can test out water circulation by using food-safe blue dye in water and check the spread color in the pool. You can do this right before changing water.

2 – Poor pH Balance in the Water

The pH balance of the water is another critical factor when it comes to algae growth. A high pH value in the water indicates greater alkalinity, which, when coupled with the lower chlorine levels, could usually cause algae growth.

Check the alkalinity of the water and make sure it’s within 7.0 to 7.6 (mildly alkaline). 

Besides Alkalinity, you should also check for the cyanuric acid and calcium levels in water. cyanuric acid is essential for maintaining the level of chlorine in pool water, protecting it from ultraviolet light.

Similarly, calcium actively works to combat the growth of algae in a swimming pool, so you should maintain it at 200 to 400 parts per million (ppm) using a test kit.

3 – Low Levels of Sanitation in the Pool

Incredibly low or inconsistent levels of chlorine in the swimming pool are probably the biggest reason why algae grow in pools.

Chlorine creates a weak acid in pool water known as hypochlorous acid, which can kill bacteria such as Salmonella, E. Coli, and other germs that cause harmful illnesses.

Swimming pools across the globe are chlorinated. Many different chlorine-based compounds are used for the process, ranging from sodium hypochlorite to chlorine gas and even chlorinated isocyanurates.

If the amount of chlorine in the water is low, it could quickly cause algae growth in the pool, so you have to maintain it at the right levels (1 to 3 ppm.)

4 – Low Water Filtration

Filtration is another crucial factor when it comes to preventing algae. Water filters remove debris and minerals that disrupt the water’s pH, encouraging algae growth.

You need to filter the water regularly and make sure that the filter is large enough, compared to the size of your pool. This ensures proper circulation and filter efficiency.

Now that you have a better idea about the causes of algae in swimming pools, let’s talk about the best methods you can use to get rid of them.

How to Get Rid of Algae in Your Pool

Manual Vacuuming Is the Best Solution

Vacuuming Can Help Decrease Algae

Most people use automated or robotic pool cleaners to keep algae out. While they’re effective for the most part, they can miss out on some spots in the pool, and that’s all that algae need to show up. 

For that reason, you should consider vacuuming the area directly yourself to make sure that it’s properly cleaned.

This allows you to bypass the filtration system and prevent any kind of recirculation of the contaminated water back into the pool.

When you vacuum manually around the pool, remember to focus on areas with dead spots so that you can get rid of algae spots.

Add Some Algaecide 

While algaecide on its own is not always effective, it’s a brilliant way to get rid of algae if you use it with other techniques in this guide. 

For instance, after vacuuming or brushing the pool, you should add some algaecide as secondary insurance so that there are no algae in the water. 

The best types of algaecides on the market include:

  • Chelated mineral (slows down algae growth)
  • High-strength polymers (stop algae growth)
  • Potassium Tetraborate (disrupts photosynthesis)
  • Phosphate remover (an essential component for algae survival)

Brush the Pool Properly

Pool Brushing Can Help Improve Algae

The algae might end up settling on the walls of your swimming pool. You need to make sure that you scrub it off the walls properly.

This way, when you add sanitizer to the mix, it’ll be able to penetrate deeply into the remaining algae.

Another advantage of brushing up the walls properly is that it helps you stir up all the sediment that was stuck to the pool walls.

A steel bristle pool brush is usually a good choice, as it works well on the walls of the pool as well as the floor. 

You’ll also need to carefully brush corners and other shaded areas in the pool, as the chances of algae growing in those spots are considerably higher.

As you continue to clean it, the water will get cloudy, which can obstruct your view. That is one of the main reasons why this technique can take a bit of time, despite being incredibly effective.

Balance the Water and Test it 

There are a bunch of different tools you can use to test out the water, including digital kits and testing strips that can determine the pH value of the water.

Make sure that you follow the instructions on each test kit to get accurate results.

When adding sanitizer to the water supply, you need to first check whether the sanitizer is effective in killing algae without heavily disrupting the water chemistry.

If you are using a poor-quality sanitizer, it’s probably not going to be enough to rid of stubborn strains of algae.

Shock Treatment

Some types of algae require shock treatment to get rid of the problem. If you haven’t used chlorine shock before or the infection is heavy, it’s best if you consider using calcium hypochlorite shock.

Stabilized chlorine isn’t a wise choice for the pool as you will probably end up with an excess of cyanuric acid. 

This will prevent the effectiveness of your stabilizer and will also allow algae right back into your pool. On top of that, it could also lead to more complicated problems.

Like test kits, the instructions here are usually detailed in the package and will help you determine the amount of formula you need depending on the size of the pool.

Filter it Out

When the shock treatment ends up killing the algae, the water in the pool is going to turn a cloudy blue. 

You will need to run the filter consistently for around 8 to 20 hours to get the algae completely out of the pool.

To speed up the process, you should consider adding a bit of pool water clarifier. 

Before you turn on the pump, it’s also recommended that you check whether the supply of water is enough or not.

Clean the Filter – Don’t Rinse It

Clean Pool Filter To Decrease Algae Don'T Just Rinse

A common mistake that most people make when it comes to cleaning out the filter is that they end up rinsing it thoroughly. 

You don’t want the filter slowly releasing particles back into the pool, which encourages algae to return to pools again.

Instead, you should consider soaking your filter in heavily diluted muriatic acid (hydrochloric acid) to get rid of the microscopic particles.

Final Thoughts

These are just a few things that you should know about getting rid of algae in your swimming pool. 

It’s going to require a bit of effort on your part, but you must take action quickly to minimize the algae from spreading.


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