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7 Reasons pH Rises Between Service Visits

A Clear Impressions Technician is testing the pH at a Client's pool.

A client recently asked, “It looks as if the pH in my pool is at 8.0 each week. I know you add chemicals weekly but each week the pH seems to be back at 8.0. What causes that?”

The second question they asked was, “How do you know the acid is ever bringing the pH down to the required level when it tests at 8.0 each week? Isn’t it possible that it needs more acid?

These are two great questions and I’m excited to share some information on this topic.

The pH level in your pool rising despite the regular addition of muriatic acid might seem counterintuitive since muriatic acid is used to lower pH. However, several factors could contribute to this outcome:

1: Alkalinity: The total alkalinity of your pool acts as a buffer for the pH. If the alkalinity is high, it can absorb and neutralize the acid, reducing its effectiveness in lowering pH. As the alkalinity adjusts over time, it might release some of the absorbed hydrogen ions back into the water, causing the pH to rise. – Because of its importance in regulating the pH, we test alkalinity at every visit and make necessary adjustments to make sure that it’s at the right level.

2: Incorrect Measurements or Dosage: Ensuring that you’re adding the correct amount of muriatic acid is crucial. Too little can have a negligible effect on pH, or it might not be enough to overcome the buffering capacity of the water. Ensure you’re measuring both the pH and the amount of acid accurately. – One of my favorite things about pool chemistry is that it’s science, not art. What I mean by this is we can use math and calculations to determine the required chemical dosages for a pool based on the chemistry readings we get when we arrive at the pool. While some pool companies estimate the amount of chemicals needed to treat a pool, we use the Orenda LSI calculator at each stop which gives us the exact dosage requirements to arrive at our targeted, balanced pool chemistry. We don’t overdose the acid when we service pools to combat higher pH because that can throw the water out of balance and create a corrosive water environment, which will shorten the life of the equipment and even etch the plaster.

3: Pool Usage and Environmental Factors: Swimmers, debris, and even rainwater can introduce alkaline substances into the pool, raising the pH. Sweat, lotions, and other substances from swimmers can also affect water chemistry. – We use chemicals to remove these substances from the pool and we test and balance the water chemistry at the pool every visit, so if the pH is higher at the time of our visit, we adjust the chemistry back into the appropriate levels.

4: Aeration: The process of aeration, whether natural or from pool equipment, can increase the pH. Aeration drives off carbon dioxide (CO2), which, when dissolved in water, forms carbonic acid. Less CO2 means less carbonic acid, resulting in a rise in pH.  –Water features such as fountains, waterfalls, and bubblers are aesthetically pleasing and can really increase the enjoyment of the pool. These water features can increase the pH of the pool through the process of aeration, so one way to slow down the rise of pH between service visits is to turn these off or slow them down when you aren’t using them.

5: Chemical Rebound: Sometimes, if the acid is not distributed evenly or if the pool is not circulated properly after the addition of acid, localized low pH spots can develop. These spots might gradually mix with the rest of the pool, leading to an overall increase in pH. – We dilute every chemical we add to the pool and pour it around the pool, no matter how benign. This helps make sure it’s evenly distributed and doesn’t sink to the bottom, resulting in plaster damage or uneven chemistry in lower-flow sections of the pool. This also results in higher efficacy of the chemicals, which helps make sure the treatment works as intended.

6: Calcium Saturation: If your pool has high calcium hardness, it might also buffer changes in pH. When you add acid, it may first react with calcium and other minerals, reducing its availability to lower pH. – Over time, calcium will rise in the pool and the only real method to remove it is through a partial drain or dilution event. That’s because calcium hypochlorite, the most common form of chlorine sanitizer, has a byproduct of adding small amounts of calcium to the pool with every treatment. We keep an eye on calcium levels and recommend a partial drain and water refresh, as needed, to make sure the levels of chemicals and minerals are in an acceptable range.

7: Salt Chlorine Generators: The reason salt systems raise pH is because of the Hydrogen bubbles off-gassing. Hydrogen gas (H2) is not the same as Hydrogen ions (H+), so it does not drop the pH. In fact, it’s the turbulence created by the off-gassing Hydrogen bubbles forces carbon dioxide (CO2) to also off-gas. As we mentioned in the section about aeration above, the loss of CO2 raises the pH of water.

One factor that is unique to Clear Impressions: We have developed a proprietary mineral treatment that helps enhance the water quality, reduce the amount of chemicals needed to balance the water, and slow down the increase in pH. We recommend this for pools with high use, prior algae issues, or consistently high pH after addressing some of the other causes listed above. This is something that benefits all pool owners and has an even greater benefit for salt water pools and for pools struggling with higher pH.

At Clear Impressions Pool Service, we take pool chemistry very seriously. Every employee takes the Orenda 4 Pillars and Orenda Academy certifications as part of their onboarding process and all of our full-time employees must either become Certified Pool Operators or Certified Maintenance Specialists before moving into a leadership position. The links to these courses are below if you’re curious about what they require.


Certified Pool Operator

Certified Maintenance Specialist

In addition to the certifications mentioned above, we hold a variety of other credentials as well. Clear Impressions’ credentials list demonstrates our unending desire to be the best and highest quality pool service company in Texas. We invest heavily in ongoing education for the entire team in order to ensure the best possible experience for all of our clients. You can find our growing list of certifications at the following link: 

Our Credentials List

If you live in our service area of SW Fort Worth and would like to get a free quote for pool care, use our website here: Get a Free Quote

Additional Reading:

We’ve written a previous blog about pH basics at the link below that might be helpful:

Orenda Technologies, a leader in pool water chemistry has also written a great blog on the topic of high pH that also might be helpful:


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