Swimming Pool pH: Definition, Ranges, How to Raise and Lower

The pH of pool water is a crucial aspect of pool and spa care. The term “pH” stands for power (mathematical) and hydrogen, and it indicates how acidic or basic a solution is. The ideal pH for pool water is considered to be 7.5, as this level prevents most water balance problems and is in line with the guidelines provided by APSP and many health departments.

pH is a measure of the relative acidity or alkalinity of water. It is a scale of 1 to 14, where 1 is extremely acidic and 14 is extremely alkaline. A pH of 7.4 is considered neutral. The pH of a pool must be between 7.2 and 7.8. pH affects the water’s corrosiveness and the effectiveness of the sanitizer.

The pH value affects the acidity or basicity of the pool water. If the pH is higher than 7.0, there are more OH– than H+, making the water basic or alkaline. Conversely, if the pH is lower than 7.0, there are more H+ than OH–, making the water acidic.

When the pH and total alkalinity of pool water are not properly controlled, it leads to several problems. For instance, water with a pH of 7.0 is corrosive to plaster and metals, causes stains, irritates eyes and skin, and decreases total alkalinity.

More acid is needed to lower the pH from 9.0 to 8.0 compared to lowering it from 9.0 to 7.0 because the pH scale is logarithmic. This means that each unit represents a tenfold difference in acidity or basicity.

The pH value impacts the overall care and maintenance of pools and spas by determining the effectiveness of the sanitizing chemicals used. When the pH is too high or too low, it causes discomfort to swimmers, damages pool equipment, and decreases the effectiveness of chlorine.

The pH level of a pool must be checked and adjusted regularly, ideally once a week. The most common method used to adjust the pH levels in pool water is by adding acidic or basic pool chemicals. Acidic pool chemicals like muriatic acid lower pH, while basic pool chemicals like soda ash and sodium bicarbonate raise pH.

Finally, the pH level of a pool affects the comfort and safety of swimmers. Water with a low pH level irritates the eyes and skin, while water with a high pH increase the chance of scaling and cloudiness.

What is an ideal pH level?

The ideal pH level for pool water is 7.5.

This is because a pH of 7.0, while considered “neutral” for water, is corrosive to plaster and metals, causes stains, irritates eyes and skin, and decreases total alkalinity. Therefore, it is not recommended to maintain this pH level in a swimming pool. Instead, the goal is to achieve a pH of 7.5, which is considered ideal for water quality. In a standard pool, the pH is maintained between 7.2 and 7.8, ideally between 7.4 and 7.6, targeting 7.5. This is in line with the guidelines provided by APSP and many health departments.

What are the signs of low ph in pool?

Signs of low pH in a pool include corrosive water, dissolved metals, etched plaster, eye and skin irritation, faster chlorine usage, a decrease in total alkalinity, stretching of vinyl liners, and blistering of fiberglass. When the pH level drops too low, it causes metal components to dissolve, leading to potential damage to pool equipment. In the case of fiberglass pools, a low pH causes the color to fade from the gel coat and lead to blisters on the surface. For vinyl-liner pools, a low pH causes the vinyl to lose color and stretch, leading to wrinkles in the liner.

How to raise pool pH?

To raise the pool pH, a method that involves aeration and turbulence is used. This is achieved by adjusting the pool returns to point upwards and running the pump at a high speed, which creates disturbance on the water surface. If the pools have standard returns, an aerator is added to the return. This method is cost-effective as air has no cost and the procedure implies minimal risk of excessively raising the pH level. As the pH nears 7.5, it requires more aeration to make a change. If the pH still needs to be increased, bicarbonate or soda ash is added. This method is efficient and increases the balance of a pool in less than a day.

Basic pool chemicals like soda ash and sodium bicarbonate are used to raise pool pH. These chemicals raise the pH level of the pool water. The amount of chemical needed depends on the current pH level and the volume of the pool. For instance, for pools with a volume of 15,000 to 30,000 gallons, adding 5 lbs of sodium bicarbonate supports the increase in pH. It is important to distribute the chemical evenly in the pool water and allow it to disperse and blend completely, which takes 1-3 hours. After this, the pH and alkalinity of the water must be tested to ensure the desired pH level has been achieved.

1. Use Aeration and Turbulence

To increase the pH of a pool through aeration and turbulence, the water needs to be effectively aerated by adjusting the pool returns to point upwards and running the pump at a high speed, which creates disturbance on the water surface. If the pools have standard returns, an aerator is added to the return. This method of aeration and turbulence raises the pH without affecting the alkalinity. This is because pH is logarithmic and alkalinity is linear, so they will never change at the same rate. Aeration removes carbon dioxide from the pool, which increases the pH without changing the total alkalinity (TA).

2. Add Soda Ash

To increase the pH of a pool with soda ash, an appropriate amount of soda ash is added into the pool. The amount needed will depend on the current pH level and the volume of the pool. For instance, if the starting pH is 7.0 and the alkalinity is 60 ppm, adding soda ash will increase the pH by 0.35. Soda ash, also known as Sodium Carbonate (Na2CO3), is a strong alkaline substance with a pH of 11.7. When added to a pool, it contributes to total alkalinity and raises the pH level. For example, adding 1 pound of soda ash to 10,000 gallons of water increases the total alkalinity by 11.3 ppm and raises the pH level. However, the exact increase in pH varies depending on the initial pH and alkalinity levels.

3. Add Sodium Bicarbonate

To increase the pH of a pool with sodium bicarbonate, the chemical is added to the pool while the pump is on. For pools with a volume of 15,000 to 30,000 gallons, 5 lbs of sodium bicarbonate must be added. It is important to weigh the bicarbonate accurately and distribute it evenly in the pool water. After adding the bicarbonate, wait 1-3 hours for it to disperse and blend completely. Sodium Bicarbonate has a pH of 8.3, so adding it to the pool water will raise the pH level. However, the increase in pH is minimal, usually by 0.04 or less.

What are the effects of low pH in pool?

Low pH in a pool increases the chance of corrosive water, dissolved metals, etched plaster, eye and skin irritation, faster chlorine usage, a decrease in total alkalinity, stretching of vinyl liners, and blistering of fiberglass. Low pH in a pool also causes the color to fade from the gel coat of fiberglass pools and leads to blisters on the surface. In vinyl pools, a pH lower than 7.2 increases the chance of the vinyl to lose color and stretch, leading to wrinkles in the liner. Furthermore, low pH makes the water corrosive or aggressive, causing it to dissolve plaster pool walls and metal parts in circulation, filtration, and heating equipment. The metals dissolved in this process later deposit as stains on the pool walls.

Is an acidic pool dangerous?

Yes, an acidic pool is dangerous. Water with a low pH level is very corrosive and causes damage or stains. Moreover, it is unsafe for swimmers as it results in eye and skin irritation, faster chlorine usage, a decrease in total alkalinity, stretching of vinyl liners, and blistering of fiberglass.

What causes low pH (alkalinity) in pool?

Acidic pool chemicals like muriatic acid causes low pH in a pool. Low total alkalinity in water also causes the pH level to consistently decrease, leading to instability. This is often referred to as pH bounce or the “yo-yo” effect. If the total alkalinity is low, any chemical added to the water significantly affects the pH level.

Furthermore, when the total alkalinity is at 90 ppm and the pH is low, the pH will naturally rise back to about 7.5 within a couple of days without a change in total alkalinity. However, it is not advisable to have a very low pH in the pool for more than a few hours as it increase the chance of metal corrosion, staining, plaster etching, and has the potential to decrease total alkalinity.

What are the signs of high pH in pool?

Signs of high pH in a pool include scale formation, metallic stains, cloudy water, short filter runs, eye and skin irritation, and poor chlorine efficiency. High pH also causes metal staining if metals are present in the water. It is challenging to raise the pH level significantly over 7.6 with aeration in a swimming pool. High total alkalinity causes the pH level to continually increase, becoming difficult to adjust the pH. When both the pH and alkalinity become too high, they cause the dissolved calcium and magnesium in the water to precipitate out as stains.

How to lower pool pH?

To lower and decrease the pH of swimming pool water, the main methods are using sodium bisulfate and muriatic acid. These chemicals are added to the pool in specific amounts based on the pool’s volume.

The pH level must be lowered when it exceeds the recommended range of 7.2 to 7.8. This range is observed by regularly testing the pool water using pH test strips or a pH testing kit.

Lowering the pool pH is important for maintaining water balance and preventing issues such as corrosion, staining, and eye and skin irritation. A pH level below 7.2 is generally considered low.

The process of “lowering pH” and “decreasing pH”” refers to the same thing, which is reducing the pH level of the pool water.

When the pH is lowered too much, below the recommended range, it is raised by adding a pH increaser such as soda ash or sodium bicarbonate. The specific amount needed will depend on the pool’s volume and the desired increase in pH.

The exact numbers for what is considered too much of a decrease in pH will vary depending on factors such as the type of pool (freshwater, saltwater, inground, aboveground) and the specific pool’s requirements. It is important to follow the recommended pH range and consult with a pool professional if unsure.

How to lower pool pH with Sodium Bisulfate?

Lowering the pool pH with Sodium Bisulfate is achieved by adding specific amounts of this dry acid per 10,000 gallons of water. The exact amount depends on the current pH level. For instance, to lower the pH from 7.8 to 7.5, the addition of 19.0 oz of Sodium Bisulfate is needed. If the pH is 8.0 and there’s a need to lower it to 7.5, the addition of 28.3 oz is required. And if the pH is 8.2 and and the goal is to  reduce it to 7.5, the addition of 37.0 oz of Sodium Bisulfate is necessary.

Sodium Bisulfate not only lowers the pH but also decreases the total alkalinity. Therefore, after adding this dry acid, adjusting the total alkalinity by adding sodium bicarbonate is necessary. Always test the pH and alkalinity of the water after making any adjustments.

When Sodium Bisulfate is added to water, it dissociates into sodium ions (Na+) and bisulfate ions (HSO4-). The bisulfate ions further dissociate into hydrogen ions (H+) and sulfate ions (SO4^2-). The increase in hydrogen ions lowers the pH of the water, making it more acidic. This process also lowers the total alkalinity of the water.

How to lower pool pH with Muriatic Acid?

Lowering the pH level of a pool with Muriatic Acid is achieved by adding a specific amount of the acid to the pool. The amount required depends on the current pH level and the volume of the pool. For instance, in a 16,800-gallon pool with a pH level of 8.0, adding 35.28 fl. oz. of muriatic acid will effectively lower the pH level to 7.5. Muriatic acid works by increasing the concentration of hydrogen ions in the water, which in turn lowers the pH level. The process involves a chemical reaction where the muriatic acid dissociates in water to form hydrogen ions and chloride ions. The increase in hydrogen ions reduces the pH level, making the water more acidic. The effectiveness of muriatic acid in lowering pH varies depending on factors such as the total alkalinity of the water.

How to lower swimming pool water pH naturally?

The Nature’s Equilibrium Method is a natural way to lower the pH in swimming pools. This method involves using muriatic acid to lower the total alkalinity of the pool water to a target of 90 ppm. This will result in a low pH, usually less than 7.0 and possibly as low as 6.0. However, the total alkalinity acts as a buffer for the pH level. If the total alkalinity is maintained at 90 ppm, it helps stabilize the pH level. When the pH is initially low, it will naturally rise back to around 7.5 over a couple of days due to this buffering effect, even without any change in the total alkalinity. This is achieved through aeration, which removes carbon dioxide from the pool, increasing the pH without changing the total alkalinity.

What are the effects of high pH in pool?

A high pH level in a pool increases the chance of several issues including scale formation, metallic stains, cloudy water, short filter runs, eye and skin irritation, and poor chlorine efficiency. This is because a high pH level leads to the water becoming too alkaline, which causes these problems. For instance, scale formation occurs when the water is too alkaline, leading to the precipitation of calcium and other minerals out of the water and onto surfaces. Similarly, metallic stains occur when metals present in the water react with the high pH and precipitate out of the water, staining surfaces. Cloudy water also results from the precipitation of minerals due to high pH. Short filter runs occur as the scale and other precipitates clog up the filter, reducing its efficiency. Eye and skin irritation occurs as the high pH has an adverse effect on the skin and eyes. Finally, chlorine efficiency diminishes because chlorine becomes less effective at higher pH levels.

Is an alkaline pool dangerous?

Yes, an alkaline pool is dangerous. High alkalinity causes the pH level to rise, leading to problems such as scale formation, metallic stains, cloudy water, short filter runs, eye and skin irritation, and poor chlorine efficiency.

What are the effects of pH and alkalinity on pool water quality?

The pH and alkalinity levels significantly affect pool water quality. Acidic pool chemicals like muriatic acid lower pH, while basic pool chemicals like soda ash and sodium bicarbonate raise pH. The rate and ease of pH change are determined by total alkalinity. Low total alkalinity causes the pH level to consistently decrease, leading to instability and corrosiveness, which damages pool walls and equipment. On the other hand, high pH levels causes scale formation, metallic stains, cloudy water, and eye and skin irritation. Therefore, maintaining the ideal pH and total alkalinity levels is crucial for pool and spa care.

The ideal pH for pool water is 7.5, and the total alkalinity is, ideally, between 80 ppm and 160 ppm. When these levels are not maintained, it leads to most water balance problems. For instance, if the pool water has a pH of 9.0, the amount of acid required to reduce the pH from 9.0 to 8.0 is ten times more than the amount needed to decrease it from 9.0 to 7.0. Therefore, achieving the perfect pH and alkalinity in pool water is crucial for maintaining water quality.

Different chemicals affect pH and alkalinity in different ways. For example, calcium hypochlorite produces an equal amount of hydroxide when added to pool water, resulting in a net pH change of almost zero. However, it adds alkalinity to the pool water. On the other hand, trichlor is acidic and will lower pH and total alkalinity.

Total alkalinity, CYA, and borate contribute to the pH buffering system in pool water, acting as buffers against both increases and decreases in pH. Therefore, maintaining the right balance of these components is also crucial for maintaining water quality.

What is pH in chemistry?

pH in chemistry is a measure of the concentration of hydrogen ions (H+) in a solution. It is used to determine how acidic or basic a solution is. The pH scale ranges from 0 to 14, with 7.0 being neutral. Values below 7.0 are acidic, and values above 7.0 are basic or alkaline. The term “pH” stands for power (mathematical) and hydrogen.

The pH scale is logarithmic, meaning each whole number on the scale is 10 times greater or less than the previous number. For instance, a pH of 6.0 has 10 times more H+ than a pH of 7.0. A pH of 5.0 would have 10 times more H+ than a pH of 6.0 and 100 times more H+ than a pH of 7.0. The pH of water decreases with an increase in hydrogen ions (H+) and increases with an increase in hydroxyl ions (OH-). The sum of H+ and OH- always equals 10-14. If there are 10-6 H+ then there must be 10-8 OH-. In pure water, which is neutral, there are equal numbers of H+ and OH– (10-7 each). If the pH is below 7.0, H+ is predominant. If it is above 7.0, OH– is predominant.

What is pool pH balance?

Pool pH balance refers to maintaining the pH level of the pool water within a specific range. The pH is a value that indicates how acidic or basic a solution is. In a standard pool, the pH is maintained between 7.2 and 7.8, ideally between 7.4 and 7.6, targeting 7.5.

What is the pH water scale?

The pH water scale is a logarithmic scale used to measure the concentration of hydrogen ions (H+) in water. It ranges from 0 to 14, with 7.0 being neutral. Values below 7.0 are acidic, indicating a higher concentration of H+, and values above 7.0 are basic or alkaline, indicating a higher concentration of hydroxyl ions (OH-). The scale was developed by S. P. L. Sørenson, a Danish chemist, in 1909. The pH of water decreases with an increase in H+ and increases with an increase in OH-. The sum of H+ and OH- always equals 10-14.

What is the importance pH for chlorinated water?

The pH of chlorinated water is crucial as it determines the proportion of free chlorine (FC) present in the forms of hypochlorous acid (HOCl) and hypochlorite ion (OCl–). The pH level affects the effectiveness of HOCl, which is the active form of chlorine in pool water and eliminates microorganisms at a faster rate than OCl–. For instance, at a pH of 7.5, the available chlorine splits evenly into 50% HOCl and 50% OCl–. Therefore, maintaining the right pH level is essential for the proper functioning of chlorine as a disinfectant in the water.

What is the importance pH for salt water?

The pH is a crucial aspect of salt water care, especially in pools and spas. It is a value that indicates how acidic or basic a solution is. Proper control of pH and total alkalinity prevents most water balance problems. For instance, if the pH of the pool water is 9.0, the quantity of acid needed to decrease the pH from 9.0 to 8.0 is ten times greater than the quantity required to bring it down from 8.0 to 7.0. The process of creating chlorine from salt in Salt Water Chlorine Generators (SWGs) results in a high pH. To reduce the pH, acid is added. Therefore, maintaining the correct pH level is essential for the overall health and balance of the pool or spa water.

How to achieve pH balance?

To achieve pH balance, it is necessary to adjust the pH to 7.5 and Total Alkalinity (TA) to 90 ppm. These adjustments are typically achieved through the addition of specific chemicals to the pool water. If the total alkalinity is high, it gets lowered by adding specific amounts of dry acid or muriatic acid. However, it is important to note that there is no chemical method to lower TA without also lowering pH. In order to increase or maintain the pH, it is not possible to chemically lower the Total Alkalinity (TA). Instead, aeration or turbulence are used to raise the pH without affecting alkalinity. Once the targets of a pH of 7.5 and total alkalinity of 90 ppm are reached, they will remain stable and will not change much.

How to test swimming pool pH levels?

To test swimming pool pH levels, pH test strip or a pool test kit are used. First, ensure the pool pump has been running for at least 1 hour. Then, collect a water sample from the pool using a clean plastic water bottle. Dip the test strip directly into the pool or spa and compare it to the provided color chart. If using a pool test kit, follow the instructions provided with the kit. After testing, record the results. If the pH is very high, the test will turn purple. If the pH is light to dark red, add the appropriate amount of muriatic acid as indicated in the instructions. Wait for 2 hours and then test the pH again. Continue testing and adding acid until the pH is 7.4.

In addition to pH, it is also important to test the total alkalinity of the water. Collect a second water sample from the pool using another clean plastic water bottle. Test the total alkalinity of the two samples using a total alkalinity test method that is accurate for 1 drop of titrant to equal 10 ppm total alkalinity.

How does pH impact pool water balance?

pH impacts pool water balance by affecting the efficiency of the disinfection process and the corrosiveness of the water. pH is crucial for maintaining the comfort of bathers, the efficiency of disinfectants, and the protection of pool system components. pH adjustment involves using different forms of acid to lower high pH levels or alkaline substances to increase low pH levels. The pH of the water also determines the levels of HOCl and OCl–, which are forms of chlorine. An appropriate pH and total alkalinity control prevents most water balance problems.