12/17/2019 | Swimming Pool & Spa | 9 MINUTE READ

Using the Best Pool Shock Chemical

people diving into a pool

A pool shock treatment occurs when an oxidant is introduced to the water in a pool, which helps to get rid of electrons in many different contaminants. When electrons are directly removed from contaminants in pool water, all pathogens, algae, and chloramines within the water are destroyed, which ensures that the pool water is effectively purified and disinfected. There are three separate chemicals that can be used for pool shock, which include calcium hypochlorite (cal-hypo), sodium di-chlor (di-chlor), and potassium monopersulfate (non-chlorine/oxidizer).

While these chemicals work somewhat differently in how they induce pool shock, they are all highly effective at creating the intended effect. In most cases, it’s recommended that homeowners use pool shock around once every week, which will allow the water to remain clean and free from impurities. Pool shock can also be used to maintain or increase chlorine levels in the water whenever necessary. If you own a pool, the following article offers an in-depth guide to the three top pool shock chemicals that you can use and how these chemicals can be beneficial to you.

Three Main Types of Pool Shock

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There are three primary types of chemicals that are used for pool shock purposes, which include calcium hypochlorite, sodium di-chlor, and potassium monopersulfate. Calcium hypochlorite is likely the most effective pool shock available because of how strong the chemical is compared to the two other options. Sodium di-chlor stays in the water longer than any other substance and includes a stabilizer that raises the levels of cyanuric acid in the pool, which reduces chlorine loss. Potassium monopersulfate is unique in that it works as an oxygen-based chemical that isn’t comprised of any chlorine. Since this chemical oxidizes the water, it enhances the positive effects of chlorine in the water.

Unlike the other two chemicals, you can swim in the pool water only 15 minutes after the chemical was added. With the other chemicals, you might need to wait anywhere from 4-12 hours until the chlorine levels have dropped back to normal. There are several Sensorex swimming pool sensors that you can use to determine when the chlorine has reached optimal levels.

The chemical that you choose for your swimming pool depends on why the water is being shocked and what the current water chemistry is. If you need to increase the amount of chlorine in your pool, calcium hypochlorite or sodium di-chlor might suit your needs. If you mainly sanitize your pool with bromine, the potassium monopersulfate might be your preferred option since it doesn’t include any chloride. It’s also possible to mix and match the chemicals that you use. Some pool owners will use a chloride-based shock chemical one week and a non-chloride chemical the next week.

Calcium Hypochlorite

Calcium hypochlorite is a highly popular substance for pool shock that’s known to be the strongest shock that you can purchase. This chemical dissolves quickly because it’s not stabilized, which means that the UV rays from the sun will burn off the chemical in a short period of time. Because of how quickly the substance dissolves, the levels of cyanuric acid in the pool won’t increase. Due to how strong this chemical is, it’s highly recommended that you pre-dissolve it before you add it directly to the pool.

While it’s possible to purchase this shock chemical from large retail and online stores like Amazon and Walmart, the strongest cal-hypo can only be purchased from swimming pool suppliers. The reason for this distinction is that most retailers have restrictions on the types of chemicals and chemical strengths that they are allowed to carry in their stores. When you use this chemical, keep in mind that it will likely increase the pH levels in your swimming pool, which you might want to measure after the shock has occurred. Since it can take 4-8 hours for chlorine levels to return to normal once this chemical has been placed in the pool, it’s recommended that you shock the pool with this chemical in the evening so that you can resume swimming the next day without issue.

Sodium Di-Chlor

Sodium di-chlor is a chlorine-based shock chemical that’s known to dissolve slowly because of its granular composition and the fact that it’s stabilized. Because of the stabilizer that’s contained within sodium di-chlor, the levels of cyanuric acid within your swimming pool will increase when you use this chemical to shock your pool. A key benefit of using this chemical to shock your pool is that it can also be used to maintain the chlorine in your pool. If you use this chemical for chlorine maintenance, make sure that you only place three ounces of the substance into the pool for every 10,000 pounds of water.

As is the case with calcium hypochlorite, you will usually need to wait at least four hours to go swimming after you’ve used the chemical, which means that it might be wise to add the chemical in the evening or just before you go to bed. This chemical won’t add any calcium to the pool water. It also has an almost neutral pH level, which means that the pH levels in your pool water shouldn’t notably increase when using sodium di-chlor. You can purchase this chemical at any retail store like Target, Amazon, or Walmart.

Potassium Monopersulfate

boy in a pool

Potassium monopersulfate is a shock chemical that’s entirely oxygen-based and isn’t comprised of any amount of chlorine, which gives it some clear advantages. This shock will oxidize your pool water and get rid of any contaminants that are contained within. The chlorine that’s already in your pool should see an increase in how effective it is once the pool has been shocked with this chemical. A core benefit of using this substance is that it dissolves very quickly and only requires that you wait 15 minutes before you start swimming once it’s been added.

This chemical also won’t alter the amount of cyanuric acid that’s contained in your pool. Some additional benefits of using this substance include not needing to pre-dissolve the chemical, effective removal of ammonia and chloramines, and the fact that it won’t damage vinyl liners. The only issue with using this shock chemical is that it’s not as effective when being used for either algae treatment or bacteria treatment. When you want to purchase some potassium monopersulfate for your pool, the best places to buy this chemical include online retailers like Amazon or any local pool supply stores.

How Often Should I Shock My Pool?

It’s recommended that you consider shocking your pool once every week if you want the pool water to remain free from contaminants. If you don’t want to go through the hassle of shocking your pool every week, the water should still be fine if you decide to do so once every month. However, going longer than this without shocking the pool means that the water will consist of high amounts of contaminants, which heightens the possibility that you or family members will become sick. If you have tested the chlorine levels in your water and find that they are too high, potassium monopersulfate can be used at any time to reduce the chlorine levels in the pool. For any reason besides shocking the pool, these chemicals can be used whenever you deem it necessary.

Why Should I Shock My Pool?

It’s very important that you shock your pool on a regular basis for a number of different reasons. For one, doing so will allow you to get rid of any small contaminants that are located in the water. This chemical also destroys pathogenic bacteria in the pool water. If you don’t shock your pool and this bacteria increases in the water, it’s possible that you would become sick from swimming. You can also shock a pool to get rid of combined chlorine molecules and to kill any algae blooms. If you want clean water, these pool shock chemicals will help you purify the water and reduce the likelihood that any swimmers are affected by the contaminants in the pool.

There are also several additional reasons why you might want to shock your pool. If your pool is comprised of a plaster surface, these chemicals can remove tough stains. If ever you discover that the chlorine levels in your pool are near or at zero, the chlorine-based shock chemicals can help you raise chlorine levels. The ability to maintain chlorine levels with pool shock chemicals can also be useful if ever you have issues with the filter or pump systems in your pool. If you see any small colonies of algae along the crevices or corners of your pool, these chemicals can be used to spot treat the areas.

Sensorex Pool Monitoring Systems

pH5000 Polycarbonate Swimming Pool pH Sensor

No matter which of these chemicals you use, the only way to be certain that contaminants are rid of and that the water chemistry in your pool is correct is by using monitoring systems to check both pH levels and ORP levels on a regular basis. ORP sensors provide you with the ability to measure the amount of chlorine in the water. On the other hand, pH sensors allow you to effectively maintain pH levels at an ideal range of 7.2-7.8. When purchasing an ORP or pH sensor, there are many options to select from.

PH5000 sensor

  • Reliably tests pH levels
  • Has a very quick response time
  • Has a durable polycarbonate body
  • Can be used immediately

S465C-pH sensor

  • Accurately monitors pH levels
  • Has an extended lifetime because of its large electrolyte reservoir
  • Accommodates pressurized applications
  • Includes a BNR connector

ORP1000 sensor

  • Is designed to measure ORP levels
  • Very easy to use
  • Long-lasting construction
  • Quick response time
  • Completely sealed

S420C Sensor

  • Offers a precise measurement performance of ORP
  • Consists of strong CPVC construction
  • Outfitted with a BNC connector that comes with varying cable lengths
  • Ideal for pressurized applications

Sanitizing Your Pool with Sensorex

When you want to effectively sanitize your pool and make sure that you always use the correct amount of chemicals, it’s recommended that you do so with the help of the many different products that we offer here at Sensorex. The chemistry of your pool can be properly monitored with an ORP or pH sensor, of which we offer several different varieties. Whether you use the S465C-ORP sensor or the S465C pH sensor, you will be able to determine how clean your pool is and how effective your sanitation efforts have been.

Visit or contact Sensorex today to learn more about the many products we offer that can help you clean your pool.

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Posted by Sensorex on December 17, 2019

Sensorex is a global leader in the design and manufacture of quality sensors for water quality and process applications. The company offers more than 2000 sensor packages for pH, ORP, conductivity, dissolved oxygen, free chlorine, chlorine dioxide, UV transmittance and other specialty measurements, as well as a full line of sensor accessories and transmitters. Its expert technical support engineers solve analytical sensor challenges with custom designs and off the shelf products.

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