Why is pH High in My Swimming Pool? Causes of a Rising pH Level and How to Lower it

A frustrating time in every pool owner’s maintenance journey is figuring out why a certain chemistry level cannot seem to remain steady.

One of those chemistry levels is pH and if is not kept in check, it can get too high and wreak havoc not only on water but also on equipment.

pH is the measurement in determining how acidic or basic (“alkaline”) pool water can get. It is based on a logarithmic scale from 0 to 14, with 7 considered “neutral”.

Ideally, the pH should be slightly more basic, around 7.2 to 8.0. This promotes better bather comfort. However, not every pool is the same.

If your water stays stable at a higher pH level, then that is OK as long as other chemistry parameters are balanced as well.

What Causes High pH Levels in a Pool?

A common occurrence and trait of pH are that it will rise over time. It is almost impossible for pH to remain stable for a whole season. Most casual swimming activities and pool chemicals will affect it in one way or another.

So, why does pH get so high in a pool and continue to rise? What do I need to look out for and how do I keep my pH more balanced? While pH generally rises naturally over time, there are a few items that contribute to high pH fluctuations:

• Water aeration
• Total alkalinity levels
• Your fill water
• A new plaster finish

Aeration of Water

Do you enjoy doing cannonballs in the pool? Do you like splashing around with your kids? These are what owning a pool is all about! You should also know this will slowly contribute to rising pH.

Simply put, splashing causes aeration and will raise pH. This also includes water features like waterfalls, spillovers, slides, bubblers, fountains, and rain.

While this should never deter you from having fun and using a pool as a pool, just keep it in mind as a potential factor in a rising pH.

Total Alkalinity Levels

Total alkalinity (TA) is pH’s buffer. It measures water’s ability to resist pH changes and prevents water from causing wild pH fluctuations. If TA is too low, pH bounce can occur. A high TA will cause pH to rise with it.

The main goal in the relationship between TA and pH is to find pH stability. While the ideal range for TA is between 50 to 90 ppm, you should find what works for your water.

pH will fluctuate less when the TA is in the right range. This may require patience and more water testing, but it will be worth the extra effort instead of chasing a rapidly rising pH.

Fill Water

Every pool will lose water eventually due to evaporation and splashing. It is common to fill up the pool with water from the tap or hose.

It is important, however, to test fill water for pH, as well as TA and calcium hardness (CH). Most tap water has a pH of 6 to 8.5, but some municipalities can increase pH levels to prevent corrosion of pipes. You could be unknowingly increasing pH every time you top the pool off.

Testing the source can help expectations of the chemistry changes.

New Plaster Finish

The age of a plaster finish will also cause pH to significantly rise over time. Owners of a newly installed plaster pool either by a new build or replaster should be aware of this fact, as any good pool builder should point it out.

As the plaster cures, it releases calcium hydroxide which has a very high pH level that can range from 9 to 11.5. Without getting too technical, the more calcium hydroxide water seeks from plaster, the higher the pH will rise.

Considering most plaster take about 28 to 30 days to cure, you can get an idea of how rapidly pH can get affected. With new plaster, you should be testing pH daily until you have a solid understanding of how it fluctuates.

If you are an owner of a new plaster finish or are getting resurfacing done soon, please refer to the National Plasterers Council 28-Day Start-Up procedure (opens a PDF).

What does High pH do to a Pool?

Maintaining a proper pH level is important for a few reasons: it promotes better bather comfort, improves the quality of the pool surface, and extends the longevity of pool equipment.

If pH is well above the normal ranges for a longer period of time swimmers can experience discomfort from eye irritation to itchy skin, and pool equipment containing metallic components like heaters can corrode faster.

Additionally, pools with plaster or concrete surfaces will start to accumulate calcium scaling which can lead to rough surfaces and can ultimately plug up filters and piping

How to Decrease pH

pH can be lowered by using either muriatic acid or dry acid. If you intend to use muriatic acid, use proper PPE: gloves, goggles, and wear a mask as the fumes can be dangerous to breathe in. Also, you want to be sure to store it in a dark, cool place away from chlorine and other sanitizers.

1. Test pH and Total Alkalinity

Since TA and pH work together, we should always test these two simultaneously. Make sure you are using a pool test kit that can accurately and reliably test these levels.

2. Measure How Much Acid is Needed

Once your pH and TA levels are tested, find out how much muriatic acid is needed based on how low you need the pH to go. Most bottles will have general guidance on how much is needed per 10,000 gallons of water.

First, you’ll need to know how many gallons your pool holds. This will give you a better idea of how many ounces or gallons of muriatic acid are needed. Use a trusted chemical calculator like Trouble Free Pool’s to know how much you need based on the pH decrease necessary.

3. Pour the Recommended Amount of Muriatic Acid into the Water

Slowly pour the amount of muriatic acid needed into the water. Ideally, this should be done in the deep end in front of a return jet so the acid can dissolve and mix quicker into the water.

Another way to add it is to dissolve it in a bucket of pool water. A good mixing ratio of water to acid is about 10:1. Never add water to acid! Always add the water first and then pour the acid in.

4. Retest to Ensure Levels are Balanced

After the muriatic acid is added, wait about 20 minutes or so until it has time to mix with the water. Retest and make sure both pH and TA are at recommended levels.

If the amount of acid needed is over half a gallon, add it in increments and retest. It’s better to underpour than to overpour, as that will then require other chemicals like borax or baking soda to raise it back up.

Finding that Sweet Spot

There are certainly other factors that can impact rising pH levels as every pool is different. This should start you on the right track to diagnose your specific problem. Start eliminating possibilities until one fits your criteria.

Keep in mind, that you should not be chasing a specific pH level; that will cause even more headaches. Let the water find its preferred pH stability and then go from there!