Calcium Hypochlorite: What Is It and How it is Used

Written by Michael Dean
November 9, 2023

bucket of calcium hypochlorite

Is it time to shock your swimming pool? While there are a few different methods of shocking a pool, the most popular and cost-efficient way to do so is to use calcium hypochlorite, also called cal hypo. Whether you are a new pool owner or looking to refresh your memory after the winter, in this article, I will cover everything you need to know about cal hypo, including what it is, how it works, when to use it, and how to use it.

Main Takeaways

  • Cal hypo is a pool shock and water sanitizer that generally contains 65% to 75% chlorine.
  • You should shock your pool every week and after a storm or a pool party.
  • Sodium hypochlorite, also known as liquid bleach, may be a better option for you if you live in an area with high calcium content in the water.

What Is Calcium Hypochlorite and How Does It Work?

Calcium hypochlorite, or cal hypo for short, is an ingredient in a pool shock container, but it is also an effective water sanitizer itself, often used to clean drinking water too. This chemical compound has been utilized since the 19th century and is one of the least costly alternatives to shocking your swimming pool.

It gets created by mixing calcium oxide (lime) with chlorine gas. The result contains a strong base, usually sold in stores as a granulated solid. It reacts well with a variety of chemical compounds, and it carries a higher pH level. One of the many reasons it is a popular product is its availability, price, ease of use, and ability to store for long periods.

So how does calcium hypochlorite work? The component of cal hypo that disinfects your pool is chlorine – it’s one of the many chlorine types you can use to disinfect your pool. Most commercially sold cal hypo products contain anywhere between 65% and 75% chlorine in the mixture. For every 1 ppm of free chlorine (FC) in your pool, calcium hypochlorite adds about 0.8 ppm of calcium into the swimming pool water. Don’t sweat the math, though. You can just use my calculator to figure out pool chlorine levels.

When the cal hypo is poured into the pool, the chlorine compounds will encounter the microbes and begin to disturb their functions. It does this by attaching to the enzymes of the microbes’ cells. Soon it will ultimately kill the bacteria by disrupting all the inner workings and destroying the cell walls. As it continues to hunt down all microbes in the water, your swimming pool will get sanitized.

It also aids in additional water treatment to minimize algae and oxidize chloramines and chemicals. A swimming pool is adequately sanitized between 1.0 and 4.0 ppm.

Calcium hypochlorite usually works most effectively at night. It contains unstabilized chlorine, which will get destroyed by sunlight. It would help if you aimed to deploy the cal hypo at dusk to wake up in the morning to a clean pool.

For more on the science of your pool, be sure to read by swimming pool chemistry 101 guide.

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In The Swim has a reliable cal hypo shock that is effective and easy to use.

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When to Use Calcium Hypochlorite in Your Pool

While calcium hypochlorite can be a reactive solution to a dirty pool, you should try to keep your pool clean. You should not wait for the disgusting chloramines to build up in the pool, but you should have a maintenance schedule and regularly add chlorine. It would be best for you to shock your swimming pool every week.

There are also unique events that will require you to shock your pool. If you recently experienced a bad storm in your area, debris could have been blown into the pool. Another time to shock your pool with cal hypo is after excessive use, such as a pool party. During this time, an extra amount of people bring in oils, sunscreens, bodily fluids, and other germs that need to be eradicated immediately.

You should also shock your pool if the pool levels have changed drastically within the last week. This water level change could leave a variety of microbes behind, which will need to get addressed through a pool shock. The best thing to do is stay proactive and ensure that your swimming pool can combat bacteria, algae, and other harmful contaminants.

Why Calcium Hypochlorite is an Effective Solution for Your Pool

Safety should always be a priority for you and your family, and it all starts with how clean your pool is. Your swimming pool must be shocked on a consistent schedule to keep your water clean and safe for the people who use it. Not only will shocking the pool raise the sanitizer level, but it will also re-energize the existing sanitizers.

When chlorine attaches to organic matter like body oils, leaves, debris, and dead skin, these harmful chemicals are created. Chlorine cannot perform its regular job effectively when trapped inside this bond. The typical pool smell you experience does not mean things are fine, but a higher level of chloramines is floating throughout the water.

Chloramines are more than an annoying compound that makes your pool smell. They can also cause respiratory problems in humans, which is another reason why it is essential to deploy Calcium Hypochlorite consistently.

How to Shock Your Pool with Calcium Hypochlorite

Not everyone’s pool is the same, so the step-by-step process will differ depending on the type of product you use and the size of the swimming pool. Besides adhering to the usage and storing instructions on the packaging, the overall process of shocking your pool with cal hypo is simple and straightforward.

The first step is gathering the necessary supplies to perform the shock. This collection of items could include the cal hypo, a 5-gallon bucket, safety goggles, closed-toed shoes, pants, long-sleeve shirts, chemical-resistant gloves, and a wooden stir stick. Make sure you put on all the necessary safety gear or have it accessible or close by.

Next, you should perform testing on your swimming pool water for TC, FC, and CC. Please ensure that you pay attention to your calcium levels if you have harder water to prevent possible hardware issues. It would help if you calculated how much cal hypo you need to add. If you did not use the math calculation, the bottle of the solution would most likely tell you how much to handle.

After you have measured the ideal amount of solution, you can fill up your bucket to 75% capacity with warmer water. Make sure to add the cal hypo to the water one pound at a time and then stir at each round of dumping. Continue to stir this consistently until the sanitizer is fully dissolved in the bucket.

It is now time to walk around the pool and pour the mixture into the surrounding edges. It would help if you dispersed it evenly and slowly. If you have any leftover residue in the bucket, you can dunk it into the water, mix it gently, and then continue walking and pouring.

I advise you to stay outside the pool for at least eight hours. If you go in too early, you can put yourself at risk for itchy skin and eyes or damage to your swimsuit. If you decide to shock the pool at dusk, this should not be too hard to abide by. But to avoid any confusion for your family or neighbors, you can sign out to let people know.

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Calcium Hypochlorite vs. Sodium Hypochlorite

Make sure you know the difference between calcium hypochlorite and sodium hypochlorite (liquid bleach). While both alternatives are proven disinfectants, there are a couple of differences. Calcium hypochlorite contains calcium, and sodium hypochlorite does not have it. Areas with higher calcium hardness levels might not react as well to calcium hypochlorite.

Not only is sodium hypochlorite calcium-free, but it also has as much available chlorine. Overall, it is a much cheaper product than calcium hypochlorite. If you live in areas with higher calcium hardness levels, this might be a better option for you in the long run.

Cal hypo is also very different from dichlor and trichlor. You can read my comparisons of cal hypo vs. dichlor and cal hypo vs. trichlor for a complete breakdown of the use cases for each.

Health and Safety Considerations for Calcium Hypochlorite

Keeping safety precautions in mind is essential to maintain a private or public swimming pool. You want to keep your pool safe and healthy, but you must always protect yourself first.

If your clothes have been contaminated with calcium hypochlorite, you should change into clean clothes. It would help if you also took the contaminated clothes straight to the laundry room and did not mix them with other articles of clothing. It would also be best to have an eyewash station or something similar close by if it gets in your eye when shocking the pool.

After you are done using the cal hypo to shock the pool, you should immediately use a wet vacuum method to clean up the areas around the pool. There is always a small chance that small traces of cal hypo will be left on the ground. Try avoiding dry sweeping as much as possible, as the dust and debris could fall back into the water.

Wrapping Up

As you can see, many components go into utilizing calcium hypochlorite effectively. When you invest time in understanding how it works and its potency, you can make your pool a safe, clean place to swim. It takes discipline and patience to shock your pool consistently, but your guests and family will thank you for such a beautiful place to swim!

Questions? Let me know, and I’d be happy to help.

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