Calcium Hypochlorite: Using Cal Hypo as a Pool Shock

Calcium hypochlorite, commonly known as cal hypo, is a powerful form of chlorine that can effectively sanitize your pool water.

However, cal hypo does not just affect chlorine levels. Let’s take a closer look into the benefits and how to use it as a chlorine sanitizer and shock treatment for your pool.

What is Cal Hypo?

Calcium hypochlorite is a chemical compound primarily composed of calcium, oxygen, and chlorine. It can come in slow-release tablet form or fast-dissolving granules.

Cal hypo in its granular form is widely used in the swimming pool industry as a pool shock and is often referred to as cal hypo shock.

How is Cal Hypo Made?

Cal hypo is an unstabilized type of chlorine, which means it does not contain a stabilizer, namely cyanuric acid (CYA), in its makeup.

Because of this, using cal hypo requires manual additions of CYA to keep it balanced. Otherwise, it will burn off faster from the sun’s UV rays.

Cal hypo can come in chlorine strengths ranging from 45-78% active chlorine strength depending on which kind is used.

Since it is made with calcium, using cal hypo will increase calcium hardness (CH) levels. If you are in an area with hard water or you have trouble maintaining calcium levels, cal hypo may not be the right choice for everyday use.

What Does Cal Hypo Do to a Pool and How Should it Be Used?

Most pool stores will sell cal hypo shock in the fast-dissolving granular form. As it comes in contact with pool water, it releases chlorine that destroys harmful pathogens, bacteria, and other chloramines ensuring that the water remains safe and clean.

Applying cal hypo is relatively straightforward, but there are some steps to take to avoid damaging or staining the pool’s surface.

• Test the water and measure out how much cal hypo is needed using our pool chlorine calculator.
• Fill a five-gallon bucket with 3/4 of pool water.
• Add the amount of cal hypo to the bucket and mix thoroughly until all granules are dissolved.
• Slowly pour the mixture in front of a return jet, preferably in the deep end.
• Immediately brush any cal hypo granules that haven’t dissolved. Leaving any on the floor or surface can damage or stain the pool.

Cal Hypo Safety Precautions

Cal hypo can be very dangerous if not used or stored properly. While it isn’t flammable, it can emit chlorine vapors in the air which can act as an oxidizer. This can ignite wood, oil, and other nearby materials.

It is very important to use as specified in its instructions. Its most commonly sold as one-pound shock bags of granular powder. The correct way to use it is to use an entire package and not leave any partially used packages lying around.

Also, cal hypo should be stored like any other pool chemical, in a safe, well-ventilated location where it can not easily get wet.

Should Cal Hypo Be Your Everyday Chlorine Choice?

The fast-acting nature of cal hypo makes it one of the more popular forms of chlorination, especially as a shock treatment. However, it is important to also know some of the drawbacks when using it and see if it is still the right choice to use.

Advantages of Cal Hypo:

• Cal hypo being unstabilized means it will not add cyanuric acid to the pool. This makes maintaining CYA levels much easier
• It comes in a stronger strength compared to other unstabilized chlorine. For example, liquid chlorine is only 10-12% and lithium hypochlorite is 35% strength.
• Cal hypo will rarely degrade over time. It can be used a few years later and still maintain the same strength as when it was newly packaged.
• It is versatile enough to be used as a daily chlorinator or as a shock treatment to address sudden water issues.

Disadvantages of Cal Hypo:

• Calcium hypochlorite is typically more expensive than other chlorines. While it may come in higher strengths, the price could make it more costly per season.
• Since it contains calcium, it will increase calcium hardness. Over time, high calcium can cause severe damage to pool equipment and plumbing if it isn’t properly maintained.

Should I Continue to Use Cal Hypo?

The decision to continue using cal hypo ultimately depends on your pool’s specific needs and your water preferences.

The main drawback is the addition of calcium. Hard water areas should not necessarily be using cal hypo on a daily basis and should consider liquid chlorine as a shocking treatment.

As always, remember to regularly test your pool water, check those calcium levels, and have fun enjoying the pool!

Frequently Asked Questions

Does calcium hypochlorite raise pH?

When it is initially applied into the water, there may be pH increase as cal hypo has a fairly high pH of over 8. However, the process of chlorine getting used up, either through sanitizing or from breaking down by sunlight, is fairly acidic in nature. When both effects are taken into account, it is more pH neutral.

Does calcium hypochlorite raise CYA?

Cal hypo will not raise CYA. It is an unstabilized chlorine which means it does not contain any stabilizer like cyanuric acid.

How much calcium hypochlorite do I need to shock my pool?

Use our pool chlorine calculator to understand how much you need during shock treatment. You will need to know your pool volume and targeted FC levels.

Can you mix cal hypo and trichlor in the pool?

Cal hypo should never be mixed with other chemicals, including trichlor. Mixing can emit toxic fumes and even cause explosions. If you choose to use cal hypo as pucks in a floating dispenser, thoroughly wash and clean it if it was previously used for trichlor tablets.