What Causes High pH In Swimming Pools & Maintaining Optimal pH Levels


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The causes of high pH in a pool include the introduction of alkaline solutions, loss of carbon dioxide, high alkalinity, temperature changes, and environmental factors such as debris and other contaminants. 

Maintaining proper water chemistry is crucial for the health and safety of your pool. One important factor to consider is the pH level. pH measures the acidity or alkalinity of the water on a scale of 0 to 14, with 7 being neutral. 

When the pH of a pool rises above the recommended range, it is considered to have a high pH. 

What Is pH & Why Is It Important In Swimming Pools?

Before we dive into the causes of high pH, let’s first understand what pH is and why it is important for pool water. pH stands for “power of hydrogen” and represents the concentration of hydrogen ions in the water. It is a logarithmic scale, meaning that each whole number change represents a tenfold difference in acidity or alkalinity.

The Centers for Disease Control and Prevention (CDC) recommends swimming pools to have a pH of 7.2–7.8, with 7.4 to 7.6 being the optimal range. They also advise that swimming pools have a free chlorine concentration of at least 1 ppm. 

What Causes A High pH In Swimming Pools?

Understanding the factors that cause high pH in a swimming pool is essential for effectively addressing the issue and preventing it from being a regular occurrence.

Introduction of Alkaline Substances

Alkaline substances are those that have a pH value greater than 7. When these substances are added to a swimming pool, they can cause the pH level to rise above the ideal range. 

Several common alkaline substances can cause the pH level to rise in a swimming pool such as baking soda, which is often used to increase the alkalinity of pool water. While adding baking soda can help to stabilize the pH level, it should be done in moderation as adding too much baking soda can lead to an excessive rise in pH, which can be difficult to correct.

Another alkaline substance that can contribute to a high pH level is calcium carbonate. This compound is often found in tap water and can be introduced into the pool through regular water top-ups. Over time, calcium carbonate can accumulate in the pool and cause the pH level to rise. It is important to regularly test the pH level of your pool water and take steps to correct any imbalances.

To prevent a high pH level in your swimming pool, it is important to regularly test the water and make adjustments as needed. This may involve adding chemicals such as muriatic acid or a pH decreaser to lower the pH level back into the ideal range. It is also important to monitor the alkalinity and calcium hardness levels of your pool water, as these can also impact the pH balance.

Carbon Dioxide Loss

When carbon dioxide (CO2) is lost from a swimming pool, it disrupts the delicate balance of chemicals in the water. Carbon dioxide is naturally present in the air and can dissolve in water. In fact, it is one of the main factors that help to keep the pH level of a pool balanced. When CO2 is lost through aeration, splashing, or agitation, the pH tends to rise, resulting in a high pH. 

One solution is to monitor and maintain the CO2 levels in the pool. This can be done by regularly testing the water with a CO2 meter and adjusting the chemicals accordingly. Adding a CO2 source, such as sodium bisulfate or muriatic acid, can help to lower the pH and bring it back into balance. It’s also important to ensure that the pool is properly ventilated to prevent excessive CO2 loss.

Another solution is to consider using alternative sanitizing methods that are less affected by pH levels. For example, saltwater pools use a process called electrolysis to produce chlorine from salt, which is not as sensitive to pH fluctuations and therefore maintains and stabilizes the pH level better.

High Alkalinity

When the alkalinity levels are high, it means that there is an excessive amount of bicarbonate ions in the water. These bicarbonate ions act as a buffer against changes in pH and can push the pH level above the desired range, resulting in a high pH in the swimming pool.

To address high alkalinity and subsequently high pH in a swimming pool, it is essential to test the water regularly. If the alkalinity level is too high, it can be adjusted by adding an acid such as muriatic acid or sodium bisulfate to lower the alkalinity and bring the pH back into the desired range.

Environmental Factors

One of the primary reasons for a high pH is the presence of mineral-rich water sources. When the pool is filled with water that contains high levels of minerals such as calcium and magnesium, the pH level tends to rise. These minerals are known as “hard water,” and they can cause an increase in alkalinity, resulting in a high pH. This is especially common in areas where the local water supply is naturally high in minerals.

Another environmental factor that can contribute to a high pH in a swimming pool is the surrounding vegetation such as trees and plants that release organic compounds into the air, which can find their way into the pool water through rainfall or wind. These organic compounds, such as leaves, pollen, and other debris, can react with the pool water and cause a rise in pH levels. Additionally, if there are excessive amounts of dust or dirt in the surrounding area, it can introduce contaminants into the pool water and contribute to a higher pH.

Pool Water (Internal) Temperature Changes

One of the main reasons why temperature changes affect the pH of a swimming pool is because of the relationship between temperature and the rate of chemical reactions. As the temperature increases, the rate of chemical reactions also speeds up, therefore any chemicals added to the pool, such as chlorine or pH adjusters, will react more quickly and potentially be used up faster. When the temperature rises, bacteria and other contaminants in the pool also multiply at a faster rate. 

To combat this, you may need to add more chlorine to maintain proper sanitation. However, higher temperatures cause chlorine to dissipate more rapidly, leading to decreased effectiveness and bacteria to thrive in the pool water.

Another way temperature changes can influence pH levels is through evaporation. Warmer temperatures lead to increased evaporation rates, which in turn can cause the concentration of minerals and other substances in the pool water to rise. This increased concentration can result in scaling on pool surfaces and equipment, as well as an increase in alkalinity.

Whether you have an inside or outside swimming pool, a preventative method to decrease evaporation rates is to use a pool cover when the pool is not in use. Pool covers not only reduce evaporation rates, but they also help to maintain chemical balance in pools.

External Temperature Changes

Another factor to consider is during periods of hot weather. During hot weather, people tend to spend more time in the water to cool off. This increased usage leads to more contaminants being introduced into the pool, such as sweat, sunscreen, body oils, and possibly, urine. These substances can alter the chemical balance of the water, leading to a high pH in a swimming pool.

To prevent temperature-related pH issues in a swimming pool, we recommend regularly testing the temperature with a temperature sensor alongside testing the alkalinity levels. 

Problems With High pH In A Swimming Pool

When the pH of pool water is too high, the effectiveness of chlorine and other sanitizing chemicals is compromised. This can lead to inadequate disinfection, allowing harmful bacteria and algae to thrive. Consequently, swimmers may be at a higher risk of waterborne illnesses and infections.

High pH can also contribute to the formation of cloudy water in pools. This is often due to the precipitation of calcium carbonate, a result of the interaction between high pH and calcium hardness. Cloudy water not only affects the aesthetic appeal of the pool but also indicates an imbalance in water chemistry.

Another issue is scaling and corrosion. High pH levels can lead to the formation of scale deposits on pool surfaces and equipment. Scaling occurs when minerals in the water, such as calcium and magnesium, precipitate out of the solution and adhere to surfaces. Over time, these deposits can cause damage to the pool walls, plumbing, and equipment. 

Additionally, high pH can corrode metal components, leading to further deterioration.

Have you ever jumped into a swimming pool and immediately felt the sting of chlorine in your eyes? Or maybe you’ve noticed that the water feels a bit too harsh against your skin. That is because high pH in a swimming pool can cause skin and eye irritations. Swimmers may experience dryness, itching, and redness of the skin, as well as eye discomfort and irritation when pH levels spike in the water. 

These symptoms can significantly impact the overall swimming experience and may discourage pool usage, it can also cause major issues if your swimming pool is for public use.

Remedies & Solution For High pH In Pools

If you have identified that your pool has a high pH level, you will need to decrease it to the optimal pH level. This can be done in several ways:

  • pH decreasers
  • Carbon dioxide off-gassing 
  • Regular water testing and maintenance 
  • Balancing alkalinity
  • Environmental management

pH Decreasers

pH decreasers, such as muriatic acid or sodium bisulfate, are commonly used to lower the pH of pool water. When adding muriatic acid you must add it safely as it is a very strong acid.

Muriatic acid and sodium bisulfate work by neutralizing excess alkalinity and reducing the pH level. It is important that when adding pH decreasers not to go overboard and cause it to become too acidic, otherwise you will need to raise the pH in the pool again. 

It is crucial to follow the manufacturer’s instructions and use the appropriate amount of pH decreaser based on the pool size and current pH level.

Carbon Dioxide Off-Gassing

A simple and natural way to lower the pH without adding chemicals is through carbon dioxide off-gassing, such as increasing aeration and water circulation in the pool. 

By promoting the release of carbon dioxide, the pH will gradually decrease. This method is particularly effective for small pH adjustments.

Regular Water Testing and Maintenance

Regularly testing the pH and other water parameters is key to maintaining proper water chemistry in your pool. Use a reliable water pH test kit to monitor the pH levels and make necessary adjustments as required. 

Additionally, ensure proper filtration, circulation, and sanitation to prevent the accumulation of contaminants that can affect pH balance.

Balancing Alkalinity

Maintaining proper alkalinity levels is crucial for pH stability. If the alkalinity is too high, it can contribute to a rise in pH. 

To balance alkalinity, use alkalinity increasers or reducers as needed, based on the test results. It is important to follow the recommended dosage and gradually adjust the alkalinity to avoid sudden pH fluctuations.

Environmental Management

Take steps to minimize the impact of environmental factors on pool water chemistry. Keep the pool area clean and free from debris to prevent the introduction of contaminants. Consider using pool covers to reduce the effects of rainfall and limit exposure to sunlight, which can contribute to pH fluctuations.

Ways To Measure High pH In A Swimming Pool 

For accurate and reliable results, we recommend using a pH meter. A pH meter is a handy tool that provides accurate and precise readings of the pH level in your pool. To use a pH meter, you simply need to dip the electrode into a water sample taken from your pool. The meter will then display the pH level on its digital screen. It’s important to follow the manufacturer’s instructions for calibrating and using the pH meter to ensure accurate readings and to ensure you know how to calibrate a pH meter correctly and how often to calibrate the pH meter.

On the other hand, if you prefer a more affordable and accessible option, pH strips are a great alternative. These small strips contain chemicals that change color based on the pH level of the water. To use pH strips, you need to dip the strip into a water sample and wait for it to change color. Then, match the color to the provided chart to determine the pH level.

Regardless of which method you choose, it’s advised to regularly test the pH level in your pool and make any necessary adjustments. 


Understanding the causes of high pH and implementing appropriate remedies will help you achieve and maintain the optimal pH range. Regular testing, proper chemical adjustments, and environmental management are key to ensuring a well-balanced pool that provides a safe and enjoyable swimming experience for all!

If you would like to know more about high pH in swimming pools or ways to manage the pH level in your swimming pool, do not hesitate to contact the world-class team at Atlas Scientific.

pH Probes & Sensors

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