Does Calcium Hypochlorite Raise or Lower pH?

Written by Michael Dean
May 31, 2023

calcium hypochlorite and pH scales

Maintaining proper water chemistry is vital for the health and clarity of pool water. A crucial factor in pool maintenance is balancing the pH level, which affects overall water quality and the swimmer’s comfort. While various chemicals are used to achieve the delicate equilibrium of pH, calcium hypochlorite often raises questions about its impact on pH.

In this article, I will explain the impact of calcium hypochlorite on pH, how to use cal hypo, and offer alternative chlorine options. Let’s dive in!

Main Takeaways

  • Calcium hypochlorite has a pH of around 10 to 12, so it can raise the pH of your pool water when it is dissolved.
  • Calcium hypochlorite is an unstabilized chlorine compound, meaning it does not contain cyanuric acid.
  • Calcium hypochlorite contains 65 to 75% chlorine.
  • Alternative types of chlorine that don’t raise pH include dichlor and trichlor.

What is the pH of Calcium Hypochlorite?

Calcium hypochlorite, commonly known as cal hypo, is a chemical compound used as a sanitizer in various applications, including swimming pools, spas, and hot tubs. Typically, when cal hypo is dissolved in water, it has a pH of anywhere between 10 to 12, although specific pH can vary according to the brand used.

It’s worth mentioning that the high pH of cal hypo can affect your pool’s pH and chlorine effectiveness as a whole. 

For example, the effectiveness of chlorine as a disinfectant is influenced by pH, with optimal disinfection occurring at specific pH ranges between 7.2 and 7.8.

Does Calcium Hypochlorite Raise pH?

Yes, calcium hypochlorite can raise the pH of the pool water when it is initially dissolved. In fact, cal hypo raises pH, alkalinity, and calcium hardness levels. The release of calcium hydroxide during the dissolution process of cal hypo contributes to the increase in pH. Calcium hydroxide is a strong alkaline substance with a pH typically ranging from 11 to 12.5. This alkaline nature of calcium hydroxide causes the pH of the water to rise, making it more basic or alkaline.

That said, even though cal hypo will initially raise the pH of your pool water, it should stabilize as the chlorine breaks down, so if you are using calcium hypochlorite as pool shock, the pH should balance after some time.

Is Calcium Hypochlorite Stabilized?

No, calcium hypochlorite is not a stabilized chlorine, which is why cal hypo is commonly used as pool shock. Stabilized chlorine, such as dichlor or trichlor, contains cyanuric acid, which helps protect chlorine from degradation due to sunlight (UV radiation).

Calcium hypochlorite, on the other hand, is an unstabilized chlorine. It does not contain cyanuric acid. This means that when calcium hypochlorite is exposed to sunlight or UV radiation, the chlorine will degrade more quickly, reducing its effectiveness as a disinfectant. This is why adding cal hypo to the pool in the evening after sunset is recommended. It is also good practice to add cyanuric acid separately afterward. Ideal CYA levels in a pool are between 30 and 50 parts per million (ppm).

Can You Shock Your Pool with Cal Hypo?

Yes, you can. Cal hypo is one of the main options pool owners have for shocking a pool. As a pool owner, shocking the pool weekly is a must! It not only boosts sanitizer levels and eliminates contaminants but also destroys chloramines, which are responsible for that telltale odor of chlorine in the pool.

Formed by treating lime (calcium oxide) with chlorine gas, cal hypo can easily disrupt bacteria and other microbes. It also has one of the highest chlorine concentrations, with most brands indicating a strength of 65-75%. Its effectiveness, reasonable price, availability, and ease of use make it an excellent pool shock.

How To Use Calcium Hypochlorite in a Pool

Here is my 7-step process on how to use calcium hypochlorite to shock your pool.

Step One: Test Your Pool Water

Specifically, test your water for free chlorine, combined chlorine, and total chlorine. And since cal hypo also raises calcium levels, check the calcium hardness levels of your pool water as well.

Step Two: Determine the Required Dosage

Like all other chemicals, Cal hypo is most effective only at the right dose. Check packaging instructions and calculate the dosage yourself to determine the appropriate amount needed for your pool. More on this below!

Step Three: Put on Protective Gear

Before handling any pool chemicals, wear appropriate protective gear, including safety goggles and gloves.

Step Four: Pre-Dissolve the Calcium Hypochlorite

Fill a clean bucket or container with water from the pool. Gradually add the required amount of calcium hypochlorite to the water, pound by pound, stirring continuously until completely dissolved. When mixing cal hypo and water, make sure to add the cal hypo to the water and not the other way around. Adding water to the calcium hypochlorite will result in a dangerous reaction.

Step Five: Pour the Solution into the Pool

Slowly pour the dissolved cal hypo solution around the perimeter of the pool. Avoid pouring directly into the skimmer or in one concentrated area to prevent localized bleaching or damage. As always, it’s best to do this in the evening hours since cal hypo is unstabilized and will be vulnerable to UV radiation during the daytime.

Step Six: Maintain Circulation

Run your pool filter for several hours to ensure thorough mixing and even dispersal of cal hypo with the water.

Step Seven: Test and Adjust Chlorine Levels

The next day, use a pool testing kit to measure the chlorine levels. It is recommended to wait until the free chlorine concentration drops back to the desired range (usually 1-3 ppm) before using the pool. Once the chlorine has fallen back to normal ranges, add cyanuric acid to stabilize the chlorine levels if needed.

How Much Calcium Hypochlorite To Use In A Pool

Determining the appropriate dosage of cal hypo is essential for maintaining proper pool sanitation and water clarity. The right amount of calcium hypochlorite ensures effective disinfection while avoiding over-chlorination, which can lead to eye and skin irritation.

Consult the manufacturer’s guidelines to determine the recommended dosage for your specific brand and formulation of calcium hypochlorite. Manufacturers often provide dosage charts or tables based on pool volume and desired chlorine levels. Adjust your calculated dosage accordingly to match the manufacturer’s recommendations.

However, as a general rule, for basic maintenance shocking, you’ll need to add 1 pound of shock per 10,000 gallons of water. Depending on the state of your pool, you might need to double, triple, or quadruple shock.

To help you calculate this, use my pool shock calculator.

Alternative Types Of Chlorine That Don’t Raise pH

There are alternative types of chlorine that don’t raise the pH level as cal hypo does.


Dichlor is a stabilized form of chlorine sold in granular or tablet form. It contains cyanuric acid, which helps protect chlorine from breaking down in the sun’s harsh UV rays. Dichlor is the only chlorine type with a fairly neutral pH, at around 6.5. This means that dichlor will barely impact or change the pool’s pH. 

Because dichlor contains cyanuric acid, the levels should be monitored when used as pool shock. Too high CYA levels can reduce the effectiveness of your chlorine.

Head to my cal hypo vs. dichlor comparison for a complete side-by-side view of these chemicals.


Trichlor is another stabilized chlorine compound that contains cyanuric acid. It is a powerful substance containing around 90% available chlorine. It is commercially available in tablet form. While dichlor is more neutral, trichlor is acidic – the opposite of cal hypo. Trichlor has a pH level of 3, so rather than raising the pH, it can lower it.

Trichlor dissolves very slowly, so it, unfortunately, cannot be used as pool shock. Instead, it is used for regular chlorine treatments.

I wrote an entire article on trichlor vs. calcium hypochlorite that you can check out for a complete comparison.

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Bottom Line

Cal hypo does influence pool pH levels by raising them slightly. Nevertheless, it remains one of the popular sanitizers among private pool owners since it is easy to use, accessible, and cost-effective. But since it can affect pH levels, just make sure to test the pH of your pool after shocking. Regularly monitoring and maintaining pH levels via weekly tests and keeping the pool well-filtered will always go a long way in keeping your pool clear and sparkling.

Do you have more questions? Shoot me a message; I’m always happy to help. And be sure to read my complete research on swimming pool chemicals.

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