Calcium Hypochlorite vs. Dichlor Comparison & Which One You Should Use

Written by Michael Dean
August 25, 2023

calcium hypochlorite vs. dichlor

Maintaining a clean and hygienic swimming pool is essential for the health and longevity of your pool. One of the critical aspects of pool maintenance revolves around selecting suitable chlorine. Among the various options available, calcium hypochlorite and dichlor are two widely used and effective sanitizing agents.

In this article, I will compare these two types of chlorine so that you can decide which type of chlorine is best for you and your pool.

Main Takeaways

  • Calcium hypochlorite is highly effective in killing bacteria and algae, affordable, and versatile.
  • Dichlor is a fast-dissolving granular substance that contains about 55 to 62% chlorine and is relatively stable, easy to use, and doesn’t raise the pH level of the water.
  • Dichlor is more suitable for sunny locations, whereas calcium hypochlorite will need the help of cyanuric acid when applied to outdoor pools.
  • Cal hypo and dichlor can both be used to shock a pool, but cal hypo is generally considered more effective.

What is Calcium Hypochlorite?

Calcium hypochlorite, commonly known as cal hypo, is a powerful and effective pool-cleaning chemical. It is also used as a water disinfectant and a bleaching agent since the 19th century. Cal hypo can come in both granular and tablet form.

Compared to dichlor, calcium hypochlorite has a higher chlorine concentration, typically ranging from 65% to 75%. This makes it a more potent and effective pool sanitizer, especially for larger pools or those with heavy usage.

Pros and Cons of Calcium Hypochlorite


  • High chlorine concentration: Calcium hypochlorite is one of the most potent pool-cleaning agents, containing about 65% to 75% chlorine. This high concentration makes it highly effective in killing bacteria and algae in larger pools or those with heavy usage.
  • Affordable: Calcium hypochlorite is generally more affordable than other chlorine types, making it a popular choice among pool owners.
  • Versatile: Calcium hypochlorite can be used for various pool maintenance tasks, including shock treatment, regular sanitization, and algae removal.
  • Contains calcium: If you have low calcium levels as well as low chlorine, cal hypo is a great way to tackle both problems at once.


  • No stabilizing agents: Cal hypo does not contain cyanuric acid, so for outdoor pools, this will need to be added separately.
  • High pH level: Calcium hypochlorite has a high pH level (10 to 12 when dissolved in water), which can cause the pool water’s pH to increase rapidly if used excessively.
  • Dangerous if mishandled: Calcium hypochlorite can be hazardous if not handled properly. It should be added slowly over the pool surface and never directly poured into the skimmer or filter.
  • Takes time to dissolve: Cal hypo is relatively fast dissolving, but you’ll still have to wait longer for it to circulate and dissolve in the water than dichlor. You’ll have to pre-mix it with water before adding it to the pool.
  • Raises calcium levels: This can be an advantage and a disadvantage. If you have too much calcium, this can lead to scaling and other issues.

What is Dichlor?

Dichlor, also known as Dichloro-S- Triazinetrione, is a type of pool shock and sanitizer commonly used in swimming pool maintenance. Dichlor is a fast-dissolving granular or liquid substance that contains about 55 to 62% chlorine. It does not come in tablet form.

When added to pool water, it dissolves quickly and releases chlorine, which helps kill harmful bacteria and algae. Dichlor is popular among pool owners because it is stabilized, easy to use, and doesn’t mess with the pH of the water like some other chlorine types.

Pros and Cons of Dichlor


  • Easy to use: Dichlor is available in granular and liquid form, and it dissolves quickly, making it easy for pool owners to use.
  • Stabilized: Dichlor contains a high level of cyanuric acid (CYA), stabilizing the chlorine and protecting it from breaking down due to UV rays from the sun.
  • Fast-acting: Dichlor dissolves quickly in water and starts sanitizing the water immediately.
  • Long shelf life: Dichlor has a long shelf life. You can conveniently store it for around five years without losing its effectiveness. This makes it an excellent option for pool owners who prefer buying bulk chemicals.
  • Does not affect pH: Dichlor does not significantly affect the water’s pH level, as it’s neutral (pH of 6.5).


  • High in stabilizer: While the high cyanuric acid level in dichlor can be beneficial in protecting chlorine, it can also lead to problems if the stabilizer level gets too high. This can cause the chlorine to become less effective and, in extreme cases, can even cause damage to your pool.
  • May not be suitable for all pool types: The high cyanuric acid content in dichlor may not be ideal for all types of pools. For example, indoor pools may not require as much cyanuric acid, making dichlor a more expensive and less suitable option.
  • Cost: Dichlor is typically more expensive than other pool chlorine products. This can make it a less popular choice for pool owners on a budget.
  • Volatile properties: Dichlor is a highly volatile chemical that requires careful handling and storage. Even a small amount of improper mixing with other chemicals, including calcium hypochlorite, can result in a potentially dangerous chemical reaction.

Main Differences Between Calcium Hypochlorite and Dichlor

Calcium hypochlorite and dichlor are two popular pool chlorine options for keeping the water clean and clear. While both are effective pool-cleaning agents, there are some differences between the two that pool owners should be aware of.

Chlorine Concentration

One of the most significant differences between calcium hypochlorite and dichlor is their chlorine concentration levels. Calcium hypochlorite contains a higher chlorine concentration, ranging from 65% to 75%, making it a more potent sanitizer. Dichlor, on the other hand, has about 55% to 62% chlorine.


Another significant difference between the two chemicals is their stabilization properties. Dichlor contains cyanuric acid, which stabilizes chlorine and protects it from breaking down due to UV rays from the sun.

In contrast, cal hypo does not contain any stabilizing agents, which means the chlorine will break down in the sun. So when using cal hypo, it’s crucial to add cyanuric acid separately. Or when shocking the pool, it must be done at night after sunset.


Dichlor has a relatively neutral pH level of around 7, whereas calcium hypochlorite has a higher pH level of around 10 to 12 when in water. This means that cal hypo will raise a pool’s pH level initially. So, pool owners using calcium hypochlorite must monitor the pH levels and adjust them accordingly to maintain proper pool water chemistry.

Suitable Pool Types

Dichlor is suitable for all types of pools, including vinyl-lined pools. On the other hand, calcium hypochlorite is not recommended to be used with vinyl pools. Calcium hypochlorite is much stronger in concentration and pH than dichlor. Cal hypo does not dissolve quickly, so the cal hypo granules can sit at the bottom of the pool and damage the vinyl liner. It is best to use dichlor or sodium hypochlorite for vinyl pools.


Cal hypo is typically much cheaper than dichlor. For example, a 25-pound bucket of cal hypo costs around $149, whereas a 25-pound bucket of dichlor costs $243.

In The Swim Calcium Hypochlorite Chlorine Granular Pool Shock

In The Swim makes a very affordable cal hypo solution.

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In The Swim Chlorine Shock Granules (Dichlor)
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Summary of Key Differences

DifferencesCalcium HypochloriteDichlor
Chlorine ConcentrationContains 65-75% chlorineContains 55-62% chlorine
StabilizationDoes not contain CYAContains CYA
pH10 to 12 when in water7
Suitable Pool TypesNot recommended to use with vinyl linersSafe to use with vinyl pools
PriceMore affordableMore expensive 

When To Use Cal Hypo In A Pool

Here are some instances when calcium hypochlorite is the best choice for your pool.

Effective Shock Treatment

Shocking the pool is necessary when the water becomes cloudy, has an unpleasant odor, or is simply not clean. It is necessary as a part of regular weekly maintenance during the pool season. Adding cal hypo to the pool water will quickly eliminate contaminants and restore water clarity. But since cal hypo does not contain CYA, make sure to only shock the pool at night!

Large Pools With Heavy Usage

If you own a large pool that is frequently used, cal hypo is the best choice for maintaining water quality. Its high chlorine concentration is particularly useful for large pools as it ensures the water is thoroughly disinfected and bacteria-free in a short period of time.

Low Calcium

If the calcium hardness levels are lower than you’d like them to be, cal hypo is a great way to raise the levels while also raising the free chlorine levels of your pool water.

Inexpensive Option

Compared to other chlorine types, cal hypo is an affordable option that doesn’t compromise effectiveness. Its affordability makes it the perfect choice for budget-conscious pool owners who still want to maintain a healthy and clean pool environment.

When To Use Dichlor In A Pool

Dichlor’s properties and features make it suitable for certain situations and scenarios. Here are some instances when using dichlor in a pool is best.

Routine Maintenance

Dichlor is an excellent choice for regular pool maintenance. It is easy to use and can effectively sanitize the pool water without causing any harm or damage to the pool equipment or surfaces. Its fast-acting nature also makes it a popular choice for routine pool cleaning. Since Dichlor contains CYA, it should not generally be used to shock the pool. If Dichlor is used to shock your pool, your CYA levels may rise to dangerous levels throughout the pool season.

Outdoor Pools

Dichlor is a stabilized chlorine, which means it contains cyanuric acid that helps protect chlorine from breaking down in sunlight. This property makes dichlor an excellent choice for outdoor pool use.

Vinyl Pools

Avoid chlorine, such as cal hypo and trichlor, if you have a vinyl pool. This is because cal hypo and trichlor are slow-dissolving and much stronger in chlorine concentration, so they can damage the vinyl liner by bleaching it and weakening it. Dichlor can be safely used in a vinyl-lined pool.

Should You Use Dichor Or Cal Hypo To Shock A Pool?

Ideally, you should use cal hypo or other unstabilized chlorine to shock a pool. If you use dichlor to shock your pool, the cyanuric acid levels will grow throughout the pool season. You can use dichlor to shock occasionally, but generally, it’s recommended to use calcium hypochlorite over dichlor as it is a more powerful shock. After shocking the pool, make sure the chlorine levels are between 1 to 3 ppm before jumping back into the pool.

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Frequently Asked Questions

Can you mix cal hypo and dichlor?

No, you can’t mix calcium hypochlorite and dichlor, as it can create a potentially dangerous reaction. Always use these chemicals separately and with caution.

What is the best chlorine for a pool?

When choosing chlorine for pool maintenance, it’s essential to consider the pool type, size, usage, personal preferences, and budget. Calcium hypochlorite and dichlor have pros and cons; the right choice ultimately depends on the pool owner’s needs and circumstances.

Bottom Line

Choosing between cal hypo and dichlor ultimately depends on pool type, size, sunlight exposure, and budget. Carefully evaluating these factors and considering your pool’s specific needs will help determine which option best suits your needs.

Regardless of the chosen chemical, follow the manufacturer’s instructions, regularly test water chemistry, and maintain proper pH levels. By making an informed decision and implementing proper pool maintenance practices, you can ensure a clean, clear, and sparkling pool for years to come!

Want to learn more about the different types of chlorine? Check out my complete guide.

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