Calcium Hypochlorite vs. Sodium Hypochlorite: What’s the Difference? (& Which To Use)

You can use many different types of chlorine to clean and disinfect a swimming pool. So, if you’re a new pool owner, you might wonder what’s the best choice. Two common chlorine options are calcium hypochlorite and liquid sodium hypochlorite. But what’s the difference between the two types of chlorine, and how do they stack up against each other?

In this article, I will go over the differences between calcium hypochlorite and sodium hypochlorite. Let’s dive in and get to know these two chemical compounds!

Main Takeaways

• Calcium hypochlorite is a type of chlorine with a concentration of 65 to 75% chlorine and a pH of 10 to 12.
• Sodium hypochlorite, also called liquid bleach or liquid chlorine, has a concentration of 10 to 12% chlorine and a pH of 11 to 13.
• Both types of chlorine are highly effective at killing bacteria, viruses, and algae.
• Main differences between the two lie in chlorine concentration, dissolution rate, pH level, shelf life, and more.

What is Calcium Hypochlorite?

Calcium hypochlorite, often referred to as cal hypo, is a sanitizer available in granular, powdered, and tablet forms. This chlorine is highly effective in killing algae, viruses, and bacteria and has a high chlorine concentration of 65 to 75%. When mixed in water, cal hypo has a pH of between 10 to 12, making it alkaline.

Pros and Cons of Cal Hypo

Pros

• Affordable: Calcium hypochlorite is a relatively affordable type of chlorine that pool owners can use on a budget.
• High concentration: Cal hypo is very high in chlorine concentration, with around 65% to 75% available chlorine. This means you can raise your pool’s chlorine levels faster and effectively sanitize the water.
• Versatile: Calcium hypochlorite can be used as a pool shock or as a general-use chlorine. Just keep in mind that if you use it for general use, you’ll also need to add cyanuric acid.
• Raises calcium levels: If your calcium hardness levels are low, cal hypo is a great way to raise the calcium levels of your pool while also raising the free chlorine levels.

Cons

• Not stabilized: Cal hypo does not contain CYA, so it is not protected against the sun’s UV rays. If you add cal hypo to a pool without also adding cyanuric acid, the chlorine will dissipate in a matter of hours.
• Does not dissolve instantly: Cyanuric acid dissolves relatively fast, but it still takes several hours to dissolve completely in pool water. So, it is not recommended to use in vinyl pools.
• High pH: Cal hypo has a high pH of around 10 to 12 when in water. So, it can quickly cause your water to become alkaline if you aren’t careful. With that said, the levels should stabilize as the chlorine degrades.
• Raises calcium levels: As the name of the chemical suggests, calcium hypochlorite contains calcium, so it can raise the calcium hardness level in your pool over time.

What is Sodium Hypochlorite?

Sodium hypochlorite, also known as liquid bleach or liquid chlorine, is a powerful sanitizer and disinfectant used in swimming pool maintenance and household cleaning. It is a liquid solution containing sodium chloride and sodium hydroxide. Sodium hypochlorite has strong oxidizing properties, effectively eliminating bacteria, viruses, and algae in pool water. It has a typical chlorine concentration ranging from 10 to 12% and a pH of 11 to 13.

Pros and Cons of Sodium Hypochlorite

Pros

• Easy to use: Since sodium hypochlorite is a liquid, it is very easy to use and can be poured directly into the pool.
• Very affordable: Liquid bleach is readily available at many pool stores and is the most affordable type of chlorine.
• Immediately dissolves: Sodium hypochlorite quickly dissolves and mixes with your pool water so it can be used in vinyl pools without the worry of damaging or bleaching the liner.

Cons

• Low concentration: Sodium hypochlorite has a low concentration of 10% to 12% available chlorine, so you’ll need quite a bit of liquid to shock or raise the chlorine levels in a larger pool.
• High pH level: Sodium hypochlorite has a high pH of around 11 to 13, so it can also cause your water’s pH level to rise. Ideally, your pool water should be a relatively neutral pH of around 7.2 to 7.6. But again, as with cal hypo, even though the pH will initially rise, it should stabilize after some time.
• Unstabilized: Like cal hypo, sodium hypochlorite is unstabilized, so you should use it with CYA to prevent the chlorine from dissipating in the sun.

Main Differences Between Calcium Hypochlorite and Sodium Hypochlorite

Let’s explore the key differences between these two types of unstabilized chlorine to help you better understand them and decide the best option for you and your pool.

Chlorine Concentration

Cal hypo has a much higher chlorine concentration at 65 to 75%, while liquid bleach is generally between only 10 and 12%.

Dissolution Rate

Calcium hypochlorite requires time to dissolve completely when added to water. In contrast, sodium hypochlorite, being a liquid, readily mixes with water upon contact. Its dissolution rate is virtually immediate, allowing quick and efficient chlorine dispersion throughout the pool.

pH Level

Both types of chlorine have relatively high pH. Calcium hypochlorite typically ranges from 10 to 12 when in water, while sodium hypochlorite has a pH of 11 to 13.

Shelf Life

Calcium hypochlorite is known for its stability and long shelf life, allowing for extended storage without significant loss of chlorine content. Properly stored, it can retain its effectiveness for an extended period. On the other hand, sodium hypochlorite, being a liquid, is less stable and has a shorter shelf life. It is more prone to degradation over time, especially when exposed to heat, sunlight, or air.

Type

Cal hypo comes in granular, powdered, and tablet forms. Sodium hypochlorite only comes in a liquid form.

Cost

The cost of calcium hypochlorite and sodium hypochlorite may vary depending on location and market factors. But as a general rule, sodium hypochlorite is considered the cheapest chlorine type and the most cost-effective. Cal hypo does come a close second, however!

When To Use Calcium Hypochlorite In A Pool

Now, let’s discuss when using cal hypo in a pool is appropriate.

General Maintenance

Cal hypo is an excellent choice for routine sanitization of pools. Its high chlorine concentration, typically ranging from 65 to 75%, ensures effective disinfection by killing algae and other unwanted contaminants and organisms.

Shock Treatment

Cal hypo is the most common type of chlorine used for shock treatments due to its high chlorine content and because it does not contain cyanuric acid. It provides a powerful and rapid dose of chlorine to eliminate contaminants, restore water clarity, and address pool issues effectively.

Low Calcium

Calcium hardness levels in a pool should be between 200 and 275 ppm if you have a concrete pool or between 175 and 225 ppm if you have a fiberglass pool. If the calcium hardness levels are low, cal hypo is a great way to bring those levels back up along with your chlorine.

When To Use Sodium Hypochlorite In A Pool

Here are the instances when using liquid chlorine would be appropriate.

Routine Sanitization

As with cal hypo, sodium hypochlorite is ideal for regular maintenance. Its liquid form allows for easy and immediate dispersion of chlorine throughout the water, ensuring effective disinfection. Regular use of sodium hypochlorite helps to kill bacteria, viruses, and algae, keeping the pool water clean and safe for swimmers. It is particularly suitable for smaller pools or those with low to moderate bather loads. With that said, sodium hypochlorite is unstabilized, so for routine treatments, you should use cyanuric acid to prevent the chlorine from breaking down in the sun within hours.

Shock Treatment

Sodium hypochlorite is an excellent choice for shock treatment because it is simple to use and starts working immediately. It provides a rapid and powerful dose of chlorine to quickly restore water clarity and eliminate contaminants. It’s recommended to shock a pool after heavy pool usage, severe weather, or as part of regular weekly pool maintenance.

Pools with Vinyl Liners

Sodium hypochlorite is suitable for pools with vinyl liners as it is not as concentrated as other types of chlorine and can distribute easily and quickly throughout the pool. This reduces the risk of having concentrated areas of chlorine, which can weaken and shorten the lifespan of a vinyl liner pool.

Inexpensive Option

While cal hypo and sodium hypochlorite are cheaper than other types of chlorine, sodium hypochlorite is the most cost-effective option. Plus, liquid chlorine is readily available everywhere.

Should You Use Sodium Hypochlorite Or Cal Hypo To Shock A Pool?

Both sodium hypochlorite and cal hypo can be used to shock a pool. What you pick is entirely up to you. However, as a general rule, using cal hypo for a stronger shock is recommended, while liquid chlorine is more suitable for general maintenance shock treatments.

Since cal hypo and liquid chlorine have vastly different chlorine concentrations, you’ll need to add significantly more sodium hypochlorite than cal hypo to oxidize the chloramines in the pool.

Another major difference is that liquid shock is added directly into the water, while cal hypo needs to be diluted in a bucket before it is added. And since sodium hypochlorite is a liquid, there’s no wait time for dissolution. On the other hand, cal hypo may be fast-dissolving, but it still needs time to fully dissolve in the pool after it’s added.

Frequently Asked Questions

Can you mix sodium hypochlorite and cal hypo?

I do not recommend sodium hypochlorite and calcium hypochlorite. Mixing these two chlorines can potentially lead to a chemical reaction, producing hazardous gases or even an explosion. To ensure safety, it is best to handle and use sodium hypochlorite and calcium hypochlorite separately, following the manufacturer’s instructions for each product. Furthermore, make sure to store them separately.

Does sodium hypochlorite contain stabilizer?

No, sodium hypochlorite does not contain stabilizer, as it does not have any cyanuric acid. When using sodium hypochlorite as a pool sanitizer, it is necessary to monitor and maintain the appropriate cyanuric acid levels separately, if needed, to ensure chlorine stability.

Does calcium hypochlorite contain stabilizer?

Calcium hypochlorite does not contain stabilizer or cyanuric acid. If needed, you can add cyanuric acid separately.

What is the best chlorine for a pool?

There’s no single “best” chlorine for a pool, as the best one for you will depend on various factors, including your preferences, the type of pool you have, and your specific needs. For example, if you have a vinyl-lined pool, you should only use dichlor or liquid bleach. If you want to shock your pool, you can use liquid chlorine, cal hypo, or dichlor. If you want something you can simply put in your automatic chlorinator, trichlor is a great pick!

Bottom Line

Calcium hypochlorite and sodium hypochlorite are both two options when it comes to chlorine in pools. While both are useful, they have slightly different applications and may be better for some swimming pools than others.

Check out my main article on swimming pool chemistry basics for more information on chlorine and other pool chemicals.

Have questions? Let me know!