Pool Shock: Granular Or Liquid

There are many different forms of chlorine you can use to shock your swimming pool in either Liquid or Granular form. After reading this blog you will understand the Pros and Cons of each type of swimming pool shock.


I had a customer a few years ago call up in a panic because they ran out of their granular Calcium Hypochlorite and it was a holiday weekend. All pool stores were closed and the customer started crying on the phone to me. They had a wedding at their house the next day and the pool was green. I told her to drive to a convenience store and buy all of the liquid bleach they have and pour it into the pool and then brush the walls to remove the dead algae. Six hours later the pool was clear and customer was very happy that the pool would be blue and clear for the wedding. Two days later she called me back thanking me for helping her during the most stressful time of her life – another customer for life!

Liquid Shock: Sodium Hypochlorite strength ranges from 5% store brands to a 12.5% commercial strength, used for many industrial purposes.

Pros: Fast dissolving, no residue, adds no calcium or cyanuric to pool.

Cons: Harder to buy, store and use. Very high pH level. Short shelf life.instant-liquid-chlorine-sm

Sodium Hypochlorite, also known as Bleach or Liquid Shock is used often at Hotel, Condo and Health Club pools, delivered by truck and stored in 50 gal vats. This commercial strength liquid chlorine is also used by laundry and dry cleaners, and is a strong concentration of 12.5 % Sodium Hypochlorite. By contrast, most store brand Bleach sold in 1 gal jugs is 5% or less – same stuff, just contains more water. If you buy liquid bleach for your pool, be sure to get unscented and unaltered, regular ol’ bleach.

When using liquid shock it dissolves very quickly and you don’t have to pre-dissolve in a bucket and then add water like you do with granular chlorine. Another advantage of using liquid chlorine is that you have no residue so you don’t have to brush or vacuum the leftover shock off the bottom of the pool. When using liquid shock be very careful when you are pouring into the pool because if you get any on your clothes it will bleach them white.

Some of the disadvantages of using liquid shock are that the commercial strength shock is difficult to find typically only pool distributors sell the liquid shock. Liquid bleach is a dangerous chemical so it is very important to make sure it is stored in a well ventilated, cool and dry area, in a container – to contain the bottles. Using Liquid shock or liquid bleach regularly will increase your pH so make sure you keep an eye on your pH and alkalinity levels.

Granular Shock: Granular or powdered oxidizers 4 types and 6 strengths.

The most common form of granular shock is called Calcium Hypochlorite, known as Cal Hypo. This type of shock is much stronger than liquid shock typically has 65 to 75 percent available chlorine. This is very easy to apply and simple to use. One of the reasons this type of granular shock is most commonly used is because it is very effective and also economical.

Another type of Granular shock is Sodium Dichloro-S–Triazinetrione which is known as Dichlor. This is a premium quality sanitizer that is perfect for both swimming pools and spas. A fast dissolving shock that will help eliminate bacteria and other contaminants from your pool or spa water without leaving much residue. This also does not affect your pH so there is no change in your water chemistry and keeps the water balanced. The Granular Dichlor has 56% of available chlorine. This type of pool shock does have to dissolved in a bucket of water.

Potassium Monopersulfate is a non-chlorine shock that is used for both pools and spas. The advantage of this type of pool shock is that is safer than a chlorine based shock. This is used to help prevent algae growth and help kill harmful organic contaminants in the pool such as bacteria. When using this non chlorine shock you can swim in just 15 minutes after shocking the pool. This type of non chlorine shock is sometimes abbreviated MPS, and works great with bromine and will not effect other swimming pool chemical levels. MPS will not raise your calcium hardness and also has a neutral pH.

Lithium Shock is another premium shock that will never bleach your pool liner. This type of pool shock dissolves immediately leaves no cloudy residue. This type of pool shock is great choice for a pool that has a heavy swimmer load or if you live in very hot climate. This product is probably one of the most expensive types of pool shock but dissolves quicker compared to Calcium Hypochlorite and in my opinion is a superior product for pool shocking.


What Is Shocking A Pool?

The term shocking means to add enough chlorine to pool or spa water to destroy all combined chlorine present in the water. This usually requires adding 10 times the amount of combined chlorine present in ( ppm). The common term for this is called breakpoint chlorination. The other reason for shocking the pool is to remove algae or bacteria, by oxidizing all contaminants in the pool. All of the shock treatments I mentioned above can be used for both purposes – for removing combined chlorine and for killing algae and bacteria.

No matter what type of pool shock you use it is very important that you follow the instructions on the label very carefully. Make sure the chemicals are stored in a cool dry place and always apply chemicals directly to pool / spa water not water to chemicals.

What’s Better – Liquid Chlorine or Granular Chlorine?

That’s your decision, but it will be decided on availability, cost and personal preference. I normally use granular shock, but when opening the pool, I like to use 5 gallons of Clorox bleach just before shocking the pool with dissolved Cal Hypo granular. When shocking clean and clear water however, I prefer to use either non-chlorine shock or Lithium shock, on my own backyard pool.




Please remember that all types of chlorine react strongly when mixed with other chlorine types or any contaminants. Never mix chlorine types, and keep them safely separated, clean, cool and dry at all times.