Acids, Bases, and pH: The Foundation of Pool Chemistry

Every day you come into contact with acids and bases. The citrus in an orange, vinegar in your kitchen, baking soda in your pantry, and even household cleaners all owe their properties to the same basic chemistry.

Pool water is no different.

Understanding acids and bases is one of the most important skills a pool technician can develop because nearly every chemical adjustment made to a pool affects its pH.

What Is an Acid?

An acid is any substance that releases hydrogen ions (H⁺) when dissolved in water.

Think of hydrogen ions as tiny particles that determine how acidic water becomes.

The more hydrogen ions present, the lower the pH and the more acidic the water.

Not all acids are equally strong. Some, like the citric acid in lemons, are mild and safe to consume. Others, like muriatic acid used in pools, are much stronger and must be handled carefully. The difference is simply how many hydrogen ions each acid releases into the water.

What Is pH?

In 1909, Danish chemist Søren Sørensen developed a simple way to measure acidity, creating what we now know as the pH scale.

The pH scale ranges from 0 to 14:

• Below 7 = Acidic

• 7 = Neutral

• Above 7 = Basic (Alkaline)

Pure water has a pH of 7.

Pool water is normally maintained between 7.2 and 7.8, where chlorine works efficiently, swimmers are comfortable, and pool equipment is protected.

One important fact about the pH scale is that it is logarithmic. A change of just one pH unit represents a tenfold change in hydrogen ion concentration.

For example:

• pH of 6 has 10 times more hydrogen ions than pH 7.

• pH of 5 has 100 times more hydrogen ions than pH 7.

This is why when we see even a small change in pH, those changes can have a major impact on pool chemistry.

What Is a Base?

Bases are the chemical opposite of acids.

Instead of releasing hydrogen ions, bases produce or accept hydroxide ions (OH⁻) in water.

Common examples include:

• Baking soda

• Soda ash

• Ammonia

• Milk of Magnesia

Just like acids, bases can be either weak or strong. Strong bases can be just as corrosive and hazardous as strong acids.

What Happens When Acids and Bases Mix?

When an acid and a base react, they undergo a neutralization reaction.

The hydrogen ions (H⁺) from the acid combine with the hydroxide ions (OH⁻) from the base to form water (H₂O).

This reaction is the foundation of pool chemistry.

When we add muriatic acid to lower pH or soda ash to raise pH, we’re controlling the balance between hydrogen ions and hydroxide ions to keep the water in the ideal operating range.

Why This Matters in Pool Maintenance

Every chemical adjustment made to a pool affects the balance between acids and bases.

• More hydrogen ions (H⁺) = Lower pH = More acidic water

• Fewer hydrogen ions = Higher pH = More basic (alkaline) water

Maintaining the correct pH is critical because it affects:

• Chlorine effectiveness

• Swimmer comfort

• Equipment life

• Surface protection

• Overall water balance

A technician who understands acids, bases, and pH understands the foundation of every other aspect of pool chemistry.

Remember this simple rule:

More hydrogen ions = Lower pH = More acidic water.

Everything else in pool water chemistry builds from this principle.

When Do You Need to Add Acid?

You should add muriatic acid when:

• pH is above 7.8

• Total alkalinity is too high (above 120 ppm)

• Scale or cloudy water is present

• Chlorine is not working effectively due to high pH

Determine the Dose

Here’s a general guideline using muriatic acid (31.45%):

Always start with less than you think you need — retest in 4–6 hours.

Add the Acid

• Turn on the pool pump to ensure circulation

• Best Practice get a bucket add pool water then pour acid into bucket ideally off of pool deck to avoid stains, mix solution then add to pool

• Never pour in one spot — This is called column pouring and can result in acid laying on the bottom and damaging the surface!  Acid is heavier than water so it will sink to the bottom unless it is mixed.

Acid Dosing Tips & Warnings