Calcium Hypochlorite vs. Trichlor: Which One Should You Use?

Written by Michael Dean
February 7, 2024

calcium hypochlorite vs. trichlor

There are many different types of chlorine to choose from, so you may wonder which one is best for you and your pool. Two of the types of chlorine you may come across are calcium hypochlorite and trichlor. While both are popular, they are vastly different and should be used for different applications.

In this article, I will explore the differences between cal hypo and trichlor to help you determine the best fit for your swimming pool.

Main Takeaways

  • Cal hypo is fast-acting, affordable, and ideal for shock treatments and indoor pools.
  • Trichlor contains cyanuric acid and is long-lasting and slow-dissolving.
  • Major differences between cal hypo and trichlor include the chlorine concentration, dissolution rate, pH level, and cyanuric acid content.
  • You should never mix cal hypo and trichlor.

What Is Calcium Hypochlorite?

Calcium hypochlorite, commonly called cal hypo, is a powerful and widely used pool sanitizing chemical due to its availability, convenience, and low cost.

This chlorine compound is often preferred for its ability to provide quick and efficient sanitization. With a chlorine concentration of around 65% to 75%, calcium hypochlorite offers a potent solution to keep your pool water clean and safe for swimming. As with all other pool chemicals, handle calcium hypochlorite with care.

Pros And Cons Of Calcium Hypochlorite


  • Fast-acting: Calcium hypochlorite quickly dissolves and raises your chlorine levels fast, ideal for treating green or cloudy pool water.
  • High chlorine concentration: With a chlorine concentration of around 65% to 75%, calcium hypochlorite can effectively kill bacteria, viruses, and algae in your pool.
  • Versatile: Calcium hypochlorite can be used to shock the pool and for regular sanitization.
  • Contains calcium: Cal hypo contains calcium, so you can raise both calcium and free chlorine levels.


  • Unstabilized: Calcium hypochlorite does not contain cyanuric acid, so the chlorine breaks down quickly in sunlight without adding CYA.
  • High pH: Calcium hypochlorite has a high pH level of 10 to 12 when in water, which can raise the pH level of your pool.
  • Raises calcium levels: While this can be an advantage, on the flip side, the calcium content can raise the calcium hardness levels of your pool to the extent that leads to scaling.
  • Not suitable for vinyl pools: Cal hypo should not be used in vinyl pools because of its high chlorine concentration.

What Is Trichlor?

Trichlor is another popular type of chlorine widely used for its convenience and effectiveness in maintaining pool water quality. Trichlor is a stabilized chlorine meaning it contains cyanuric acid, which helps slow down chlorine degradation in sunlight.

With a chlorine concentration of around 90%, trichlor offers a highly effective sanitizing solution for your pool. This chlorine comes in tablet form and is placed in a floating dispenser or automatic chlorine dispenser for continuous chlorination. Trichlor has a low pH of 3.

Pros And Cons Of Trichlor


  • Effective sanitization: Trichlor contains a high concentration of chlorine, typically around 90%, which makes it a powerful sanitizer. It effectively eliminates bacteria, viruses, and algae, ensuring clean and safe pool water for swimming.
  • Long-lasting: Trichlor has a relatively long shelf-life, so it’s a great choice for those that prefer to buy their chlorine in bulk.
  • Slow-dissolving: Trichlor tablets are designed to dissolve slowly in pool water, providing a continuous and consistent chlorine release over time. This slow-dissolving feature makes it convenient for pool owners as they don’t have to add chlorine as frequently.


  • pH and cyanuric acid imbalance: Continuous use of trichlor can lead to a gradual decrease in pH levels and an increase in cyanuric acid levels in the pool water. Never use trichlor in indoor pools.
  • Not suitable for vinyl pools: Trichlor’s acidity, high concentration, and slow dissolving nature can damage to vinyl liners if not used carefully.
  • Not suitable for shocking: Trichlor cannot be used to shock a pool.

Main Differences Between Calcium Hypochlorite and Trichlor

Let’s explore the main differences between cal hypo and trichlor.

Chlorine Concentration

Calcium hypochlorite typically has a chlorine concentration ranging from 65% to 75%. And trichlor has a much higher chlorine concentration, around 90%.

Dissolution Rate

Cal hypo dissolves much faster than trichlor. Cal hypo dissolves entirely in about 4 to 6 hours. Trichlor is a slow-dissolving chlorine placed into a chlorine dispenser and slowly released over time. A single trichlor tablet can last 3 to 7 days.

pH Level

Cal hypo has a pH of 10 to 12 when in water, making it alkaline. On the other hand, trichlor is acidic, with a pH of just 3. Regular monitoring and adjustment of pH levels are essential when using both. The pH level of your pool should be between 7.2 and 7.8.


Cal hypo is available in granular, powdered, or tablet form and is usually dissolved in water before adding to the pool.

Trichlor is found in tablet form only and is designed to dissolve slowly in pool water.

Cyanuric Acid Content

Cal hypo does not contain any cyanuric acid, whereas trichlor is a stabilized chlorine, meaning it contains CYA.

Key DifferencesCalcium Hypochlorite Trichlor
Chlorine Concentration65% to 75%Around 90%
Dissolution RateFasterSlower
pH Level10 to 12 when mixed with water3
TypeGranular, powdered, or tabletTablet
Cyanuric Acid ContentDoes not contain CYAContains CYA

When To Use Cal Hypo In Your Pool

Here are some situations when cal hypo is the best option for your pool.


Calcium hypochlorite is an excellent choice for pool shock treatments. It can quickly raise chlorine levels and eliminate bacteria, algae, and other contaminants in your pool water.

Indoor Pools

Since calcium hypochlorite contains no cyanuric acid, it’s best suited for indoor pools where UV rays can’t break down chlorine levels. Alternatively, if you use cal hypo for an outdoor pool, make sure to use it at night and add CYA separately.

Low Calcium Hardness Levels

The calcium hardness levels of your pool should lie somewhere between 175 and 225 ppm for a fiberglass pool or 200-275 ppm for a concrete pool. If the levels are low, cal hypo can be a way to raise those levels slightly while also raising your chlorine levels.

Stabilizer Control

CYA helps prevent chlorine degradation due to sunlight exposure. However, excessive stabilizer levels can hinder the chlorine’s effectiveness. Cal hypo can be used when stabilizer levels are too high, as it does not contribute to the accumulation of cyanuric acid. By using cal hypo in these situations, pool owners can restore the balance between chlorine and stabilizer, optimizing the disinfection process.

When To Use Trichlor In Your Pool

Here are some instances when trichlor is the recommended choice for pool maintenance.

Continuous Chlorine Sanitization

Trichlor is designed for slow-release chlorine sanitization. It is often used in floating dispensers or automatic chlorinators, where it dissolves gradually to provide a consistent chlorine level over an extended period. This makes it suitable for regular and automated sanitization. The slow-release nature of trichlor eliminates the need for frequent manual dosing, making it a popular choice for pool owners seeking convenience.

Outdoor Pools

Unlike calcium hypochlorite, trichlor contains a stabilizing agent that helps protect chlorine from degradation caused by sunlight. This makes it an ideal option for outdoor pools exposed to UV rays.

Low Cyanuric Acid Levels

Similarly, if you have low cyanuric acid levels in your pool, trichlor can quickly raise those levels to an appropriate level, helping to protect the chlorine from the sun.

High pH

Trichlor is acidic with a pH level of 3, so if you have high pH, trichlor may be able to help. However, since trichlor is a slow-release chlorine, if you need to fix your alkaline water as soon as possible, it would be better to opt for sodium bisulfate or muriatic acid. On the other hand, do not use trichlor if you already have acidic water.

Should You Use Trichlor or Cal Hypo To Shock Your Pool?

Cal hypo is a better choice for shocking your pool due to its fast-acting nature. It can quickly boost chlorine to address issues like algae blooms or bacteria. Always follow the manufacturer’s instructions for proper dosing and application when using cal hypo for shock treatments. 

With its slow-dissolving nature, trichlor is better suited for regular chlorination and cannot be used for shock treatments.

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Frequently Asked Questions

Can you mix trichlor and cal hypo?

Never mix two chemicals, including trichlor and cal hypo, as doing so can cause a chemical reaction and release harmful gases. 

Does trichlor have a stabilizer in it?

Yes, trichlor contains stabilizer (cyanuric acid). Cyanuric acid helps slow down the degradation of chlorine due to sunlight exposure. Trichlor’s built-in stabilizer content makes it a suitable choice for outdoor pools exposed to sunlight for extended periods. 

Does cal hypo have stabilizer in it?

Calcium hypochlorite does not contain stabilizer. You use cal hypo for an outdoor pool, but you’ll will need to add cyanuric acid separately or shock the pool at night.

What is the best chlorine for a pool?

The best chlorine for a pool depends on various factors, including pool type, usage, and personal preference. Both calcium hypochlorite and trichlor are popular choices for pool sanitation. Cal hypo is often preferred for its quick sanitization and ability to be used as shock treatment. On the other hand, trichlor is valued for its convenience.

Bottom Line

Choosing the right pool-cleaning chemical is essential for maintaining a clean and safe swimming pool. When comparing calcium hypochlorite and trichlor, it’s crucial to consider their differences and suitability for different pool maintenance needs.

Do you have more questions? Let me know!

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