Understanding Pool pH & Total Alkalinity

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If you want to keep your swimming pool chemistry steady, it’s essential to understand the relationship between pH and total alkalinity. 

Total alkalinity and pH work hand in hand. Keeping the total alkalinity in your pool at the ideal levels of 80 to 120 ppm can help keep your pH level steady at the ideal levels of 7.2 to 7.46. 

Keeping pH and total alkalinity in check is essential to prevent chemistry fluctuations, eye irritation, skin irritation and rashes, ineffective sanitization, ruined pool surfaces, corrosion, scaling, and clogged pipes and filters.♡

What Is pH?

When you see a pH scale, the pH measures the “potential for hydrogen” in a chemical substance. The scale shows how acidic or alkaline (sometimes called base) the substance is. 

When you look at a pH scale, you will see that it goes from a low of zero to a high of 14. Each number, pH and alkalinity, are measured in parts per million (ppm), which refers to the concentration of minerals and soluble matter in the substance.

Understanding what the numbers on a pH scale mean can help you tremendously in pool maintenance. 

Neutral = pH of 7.0

If a substance has a pH of 7.0, it’s completely neutral without any acidity or alkalinity. 

We think of pure water as having a pH of 7.0. 

Acidic = pH of 0 to 6.0

Below a pH of 7.0, a substance is more acidic. The closer a substance is to zero, the more acidic the substance is.

Some examples of acidic substances include citrus fruits, soft drinks, stomach acids, and vinegar.

Alkaline = pH of 8.0 to 14.0

Likewise, above a pH of 7.0, the substance is more alkaline. The closer a substance is to 14.0, the more alkaline the substance is.

Some examples of alkaline substances include bleach, ammonia, dishwasher soaps, and disk batteries.

pH Measurement Magnitude

When you think about pH, it’s necessary to understand that the scale is logarithmic, meaning that each whole number represents a difference in magnitude. 

For pH, every number on the scale is ten times more or ten times less than the number beside it. 

For example, water with a pH of 8.0 is ten times more alkaline than water, with a pH of 7.0. On the other hand, water with a pH of 6.0 is ten times more acidic than pure water.

How Is pH Important for Pool Chemistry?

The pH level of the water in your pool has a dramatic impact on free chlorine’s (FC) ability to sanitize your pool. 

The higher your pool water’s pH, the more effective it is at sanitizing contaminants from your pool.

If your pool water has a pH of 8.0, FC only sanitizes with 20% effectiveness. You also don’t want your pool water to go higher than 8.0 because more alkaline water can cause skin rashes.

Decreasing the pH to 7.0 increases the FC’s effectiveness to 66%. So, if you lower the pH even more, it would make the FC more effective at sanitizing your pool, right? Sure, but that doesn’t mean it’s a good idea. Keep in mind that the lower the pH, the more acidic the water will become. Anything lower than 7.0 will cause skin irritation and sting swimmers’ eyes like getting acidic citrus juice in them would.

What Is the Ideal pH Level in Your Pool?

The CDC recommends pool pH levels of 7.2 to 7.8, with the ideal pH being 7.2 to 7.6. At this level, the pool water is non-corrosive, comfortable to swim in, and can sanitize effectively. Thus, it’s imperative that you check your pool’s pH regularly.

Low pH Side Effects

  • More acidic water irritates the skin and eyes

High pH Side Effects

  • FC is less effective at sanitizing the pool
  • More alkaline water can cause skin rashes

How Can You Change pH in Pool Water?

To understand pH better, it’s good to know what’s happening to your pool to cause pH changes and what you can do to adjust it.

Low pH (Acidity) Causes

  • Adding too much pH reducer
  • Local water with a low pH
  • Natural pool contaminants from heavy pool usage (saliva, body oils, sweat, urine, etc.)
  • Foreign organic matter in the pool (grass, insects, dirt, etc.)
  • Rain pH
  • Shocking your pool

How to Raise Low pH

If your pool’s pH is too low, you can use the following substances to raise it:

  • pH increasers
  • Soda ash 
  • Adding new water (hose water is usually more alkaline than pool water)

High pH (Alkalinity) Causes

  • Local water with a high pH
  • Adding too much pH increaser

How to Lower High pH

If your pool’s pH is too high, you can use the following substances to raise it:

  • Muriatic acid
  • Sodium bisulfate (dry acid)

What Is Total Alkalinity?

pH and total alkalinity are completely different. While a pH scale can measure alkalinity, it does not measure total alkalinity.

Your pool water’s total alkalinity measures the concentration of alkaline substances dissolved in it. Total alkalinity also measures the water’s ability to resist pH change. 

Alkaline substances in your pool both attract and release hydrogen ions. These alkaline substances buffer against changes in pH because of the way they interact with hydrogen ions.

How Alkaline Substances Benefit Your Pool

When acid contaminants enter your pool, the alkaline substances in your pool neutralize some of the acids.

As you saw above, most pool contaminants are acidic, including rain, body contaminants like urine, and organic matter like dirt that people track into the pool. The chlorine solution that you use to sanitize your pool is also acidic. For reference, urine has a pH of 6.0, and sanitizers like Trichlor have a pH of 3.0. 

Thus, alkaline materials like cyanuric acid in your pool are essential to buffer your pool water from acidic contaminants that are constantly entering your pool. 

Most people already use cyanuric acid in their pools as a chlorine stabilizer. It forms a weak and temporary bond with chlorine, which helps protect the chlorine from the sun and absorb UV light. However, its ability to bind with chlorine also makes it a buffer to keep pH high.

What Is the Ideal Total Alkalinity Level in Your Pool?

Keeping the total alkalinity level in your pool at the right level will keep your pH stable. The CDC indicates that the ideal total alkalinity level in your pool is 80 to 100 ppm. However, some sources suggest keeping it as high as 120 ppm. At this level, the total alkalinity both buffers and stabilizes the pool water, allowing the FC to effectively sanitize the pool water.

Low Total Alkalinity Side Effects

Side effects of low total alkalinity include: 

  • Ruining pool walls and surfaces
  • Corrosion of metal components in your pool
  • Making pool sanitizers less effective
  • Fluctuating pH

High Total Alkalinity Side Effects

Side effects of total alkalinity that is too high include:

  • Water scaling as particles come out of solution and deposit on pool items
  • Reduced water circulation, clogged filters, high water pressure, and reduced pool pump lifespan as a result of scaling 
  • pH change resistance, which can make FC less effective at pool sanitization

How Can You Change Total Alkalinity in Pool Water?

There are a few substances that you can use if you need to raise or lower the total alkalinity in your pool.

Raising Total Alkalinity

The most popular chemical substances that people use to raise total alkalinity in a pool are:

  • Sodium bicarbonate (baking soda)
  • Alkalinity increaser product (be sure it contains sodium bicarbonate)

While cyanuric acid is a part of the picture of the total alkalinity in your pool, you should keep it between 30 and 50 ppm in your pool. The higher the levels of cyanuric acid in your pool, the weaker your chlorine will become, which is why we don’t suggest adding more cyanuric acid to raise alkalinity in your pool. While some people do keep cyanuric acid levels as high as 80 ppm, the World Health Organization discourages letting levels exceed 100 ppm.

Lowering Total Alkalinity

The most popular chemical substances that people use to lower total alkalinity in a pool are:

  • Sodium bisulfate (dry acid)
  • Muriatic acid

Re-Checking Total Alkalinity and pH

It’s important to let the pool sit for six hours before retesting. You will also want to check the pH level in a pool after using these substances because they can change a pool’s pH levels as well as the total alkalinity.

Final Thoughts on pH and Total Alkalinity in Your Pool

Test strips are essential to keep a check on pH and total alkalinity. 

You should be checking your pool chemistry two to three times a week and after weather events. If you’re a new pool owner, it’s a good idea to check chemistry daily or after events like swimming or rain to understand how your pool chemistry changes with acidic contamination.

Keeping the total alkalinity in your pool at an ideal level of 80 to 100 ppm can help prevent your pool pH from fluctuating wildly during these events and prevent you from spending a lot of time wrangling chemicals. A little prevention can make you a happier pool owner.

Questions and Answers

Should I adjust pH or total alkalinity first?

You should adjust alkalinity first and pH second.

What is the relationship between total alkalinity and pH?

Alkalinity is a liquid’s resistance to pH change. pH is the measurement of a liquid’s acidity. When alkalinity is high, the liquid will have a strong resistance to becoming more acidic or less acidic. When alkalinity is low, pH can change very easily.

Is total alkalinity the same as pH?

No, total alkalinity and pH are not the same. The pH value is the measurement of the acid. Alkalinity prevents change to the current pH value.

Does adding chlorine increase the pH?

Chlorine doesn’t remove any hydrogen from the pool, but it will cause the readings to raise slightly and temporarily. Within two to three days, the pH readings will lower back down to where they were before the chlorine was added.

Is it safe to swim in a pool with low alkalinity?

While it is very unlikely to cause any serious health problems, it isn’t a good idea. If the alkalinity is low, the pH can swing from one side of the spectrum to the other with little resistance. If it swings to the corrosive side, you might notice your eyes start to burn and the acid will eat away at your pool.

Does muriatic acid lower pH?

Yes, muriatic acid will lower pH. Pool owners often use muriatic acid to lower the pH and alkalinity in their pools.

Does raising alkalinity raise pH?

If alkalinity is too high, the pH will continually climb.

How do I aerate my pool to raise the pH?

Aerating your pool is easy and can be very cheap. You can use fountains, waterfalls, or small nipple fittings. Most aerators are plug-in-play devices that simply need to be secured to your return line.

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