There are two main ways to lower the pH level in a pool. The two chemicals used to dose swimming pools and decrease pH are sodium bisulfate and muriatic acid.
Has the pH level inside your pool spiked? If pH levels remain too high for too long, it causes issues for bathers and pool equipment. Pool chemicals will need to be added as soon as possible to lower the pH level to a normal level.
Whether you are working with swimming pools, or you have the luxury of owning a pool at home, maintaining appropriate chemical balances in the pool water can often be challenging, yet necessary. Many people find basic water chemistry a tricky concept to control, and it starts with the unknown of how to balance pH levels in the water.
In this article, we’ll go through the safest way to lower the pH of pool water, why the water may have become more alkaline, and how you can prevent it from happening again.
When we talk about pool pH, we are referring to whether the pool water is basic (alkaline) or acidic. The pH scale runs from 0 to 14, where anything greater than 7 is alkaline, and anything lower than 7 is acidic.
The pH of pool water is best maintained at a range of 7.4 to 7.8, or slightly alkaline. If the pH level drops below 7.4 or exceeds 7.8, action is required to alter the pH back to the ‘normal’ range.
Total Alkalinity And pH
Total alkalinity and pH go hand in hand, as it is the alkalinity in the pool water that keeps the pH level stable. Without alkalinity as a buffer, the pH level in a pool would constantly fluctuate.
For example, if the total alkalinity drops, the pH level inside your pool would become unstable. However, when the total alkalinity rises, it increases the pH level with it.
This is why it is essential to adjust the alkalinity level inside the pool water before adjusting the pH. When the total alkalinity level is too high, a pH decreaser such as sodium bisulfate is used to lower both the alkalinity and pH level. Whereas, when the total alkalinity level is too low, yet the pH is greater than 6.8, an alkalinity increaser is added to the water.
Ideal Pool Total Alkalinity Levels
The total alkalinity in pool water should be between 100 and 150 parts per million (ppm).
What Causes High pH In Pools?
Many factors increase the pH level in a pool:
Algae Growth: As algae consume carbon dioxide (CO2) from water and CO2 is an acidic compound, the decrease in CO2 levels can cause the pH level to rise.
Pool Shock: Calcium hypochlorite (chlorine) has a very high pH level, so, if you’ve shocked your pool with this inorganic compound, pH levels can spike and the calcium hardness level can increase, causing the water to appear cloudy.
Accidentally Dosing With A pH Increaser: It could be that you have accidentally mixed up the chemicals, and have added a pH increaser instead of a pH decreaser. Always label the chemicals to prevent dosing mistakes.
Adding Water With A High pH: Always test the pH and total alkalinity of the water used to top off or fill your swimming pool to ensure that it is not too basic.
Installing Too Many Water Features: Swimming pools look fantastic with water features such as fountains or water slides, but the issue is they create a lot of water movement. Increased water movement increases the aeration and outgassing of CO2, raising the pH level of the water over time.
High Salt Content In A Pool: Some places use seawater or saltwater generators in their pools, which can increase aeration from bubble formation.
Replastering Pool Surfaces: Calcium hydroxide is the main component found in cement-based plaster. Newly plastered pools can release calcium hydroxide for up to four weeks, increasing the pH of the pool water as it is absorbed.
Problems With High pH In Pools
Pool water that has a pH greater than 7.8 is considered high. If the pH remains high for a long period, the number of issues associated also increases.
High pH reduces the effectiveness of chlorine, which is an essential chemical for maintaining water quality and effectively killing microbes. When the pH is high, more chlorine will be required, which affects the chemical balance in the pool water.
Just like acidic pool water, water that has a high pH can irritate the eyes and skin of swimmers and bathers. Not only is high pH linked to personal issues with users, but it also affects swimming gear. High pH levels erode swimwear and goggles much faster than pool water with a balanced pH level.
In addition to user equipment being damaged, high pH levels damage pool equipment from calcium scale build-up.
So, the first step in solving the above issues is to test the pH of the pool water.
How To Test pH Levels In A Pool?
It is super easy to test and monitor pH inside a swimming pool.
The most accurate way to measure pH levels in water is with a pH sensor/meter. However, basic pH testing strips can also be used. If you are using a pH sensor/meter, take the pH test kit and submerge the pH probe into a water sample taken directly from the swimming pool.
Once the pH probe has finished measuring the pH level, the pH value is displayed on the pH meter.
Sodium bisulfate and muriatic acid are the two main chemicals used to lower the pH of pool water. In most pool shops and online, these chemicals are called pH reducers or pH minus products. So, if there is a preferred chemical you wish to use, always check the content label before purchasing.
Also known as “dry acid”, sodium bisulfate is a fine powder commonly used to lower the pH in pools. Sodium bisulfate is typically preferred over muriatic acid due to its safer use and ease of storage. However, as it is a powder, you should avoid using it on very windy days. The pH level of sodium bisulfate is 1.2-1.3.
Muriatic acid, more commonly called “hydrochloric acid”, is a strong pH decreaser because of its low pH (pH: 1.0). Muriatic acid comes in a liquid form, making it easy for dosing pool water.
Both sodium bisulfate and muriatic acid have very acidic properties, so there are a few safety tips that you must follow when working with them.
Safety Tips When Using pH Reducer Chemicals
Both muriatic acid and sodium bisulfate can damage the surface of your skin and the surrounding pool surface. Therefore, you must always use caution when handling.
When working with pool chemicals, you should:
Wear protective equipment such as gloves, goggles, and clothing that fully covers your skin
Never mix them with chlorine – mixing chemicals produces toxic fumes which are harmful
Always add the chosen acid to a plastic bucket of water – you must always add the water to the bucket first when mixing pool chemicals, not the other way around
Never use the pool immediately after water treatment – always wait a few hours before bathing or swimming in the pool
A Step-By-Step Guide To Lowering pH In A Pool
Before altering the pH of water in a pool, you must always test the pH level to work out how far off the ideal pool pH level is. You must also make note of the total alkalinity in the pool to ensure the correct dose of acid is added.
Next, calculate the water volume in your pool so that you measure the correct amount of acid dosage. If you already know the volume of the pool in gallons, that’s great! But, if you don’t, do not worry as we have some easy mathematics to work it out.
With a tape measure, measure the length (L), width (W), and depth (D) of your pool. If your pool has different depths, take the average depth of the pool.
Use the following equation: ((L x W) x D) x 7.5
With a tape measure, measure the diameter (D) of the pool.
Use the following equation: (D x D) x 5.9 – the diameter is multiplied by itself first.
We recommend measuring the depth in feet (ft). If using another measurement unit (such as meters), keep it the same throughout the calculation.
Once you have the pool volume, current pH level, and total alkalinity readings, you can now measure the amount of acid required to lower the pH level.
The easiest way is to use an online pool chemistry calculator, but if you prefer to calculate the acid dosage yourself, below are the general dosage guidelines.
Per 10,000 gallons of pool water:
Sodium Bisulfate: 5-7 ounces to lower pH by approx. 0.1
Muriatic Acid (15% strength): 10 ounces to lower pH by approx. 0.1
Muriatic Acid (31% strength): 5 ounces to lower pH by approx. 0.1
When adding acid to pool water, it’s likely the total alkalinity will also drop. This is normal and unavoidable, but do not panic as we will help you resolve this later on.
With the correct amount of acid measured out, it is ready to be added to the pool water. If you are worried you will overdose your pool water with acid, be conservative and only add 75% of the measured amount of acid. If it isn’t enough, you can always add more after.
Remember: Always wear protective equipment when working with acids and toxic chemicals.
As muriatic acid is a liquid, you can pour it directly into the deepest part of the swimming pool, ideally near an active return jet to evenly distribute the acid. Some people prefer to add muriatic acid to a bucket with pool water to dilute it, this is not necessary, but there is also no harm in dosing the pool this way if it makes you more comfortable.
As sodium bisulfate is a powder, you will need to mix it with pool water in a plastic bucket before adding it to the pool water. Once the granules have fully dissolved, pour it into the deepest part of the pool, and just like dosing with muriatic acid, pour the acid near an active return jet if possible.
After 15-20 minutes, retest the pool water with a pH test strip or electronic pH test kit (pH meter/probe). If you have accidentally turned off the pool pump, you will need to wait slightly longer to test the water.
Upon testing the pH level of the pool, you should see a much lower total alkalinity and pH level than before treating the pool with acid. Hopefully, the pH and total alkalinity levels are within the ideal range for pools. If it is still too high, add more acid.
At this stage, you want to focus on the pH level, as total alkalinity can be raised if it is lower than 100-150 ppm afterward.
If the pH or total alkalinity has dropped too low, add a small amount of soda ash or baking soda. If you are unsure how to do this, you can read our guide to raising pH and alkalinity pool levels.
Tips For Maintaining Pool pH
If your pool continuously suffers from a high pH, there are a few tips to help keep the pH level balanced and the need to frequently lower the pH.
Test the pool water frequently with a pH test kit – we recommend at least twice per week
Keep the swimming pool clean and well-sanitized to prevent chemical imbalances
Only shock the pool when necessary, as high amounts of chlorine are associated with rising pH
Measure the pH of the water source because the water from some areas may have a higher mineral content than others which could alter the pH of the pool
If your pool water has a high pH, do not worry, as two chemicals are used to lower the pH (sodium bisulfate and muriatic acid). As sodium bisulfate and muriatic acid are both strong acids, caution must be taken and proper handling techniques should be followed.
Remember that water chemistry can be challenging. However, if you keep your pool well-maintained and clean, you are less likely to run into problems.
For any questions regarding the pH of water, or what water chemistry testing kits we offer, do not hesitate to contact the world-class team at Atlas Scientific.
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