What You Need to Know About Shocking Your Pool

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What You Need to Know About Shocking Your Pool

Sometimes, when you do something on a regular basis, you tend to do it on automatic, without thinking about if there’s possibly a better way of doing it – or if you’re even doing it right to begin with! Such can be the case when you’re shocking your swimming pool. Seasoned pool owners may have gotten into one routine without knowing if it’s the best method for the condition of their pool water at that particular time, or if they’re using the best type of shock.

Now that we have you considering your pool shocking routine, here’s what you need to know!

Pool Shocking – A Brief Definition

“Shocking” refers to the process of adding chlorine or non-chlorine pool chemicals to the water in order to raise the “free chlorine” level. The goal is to raise this level to a point where contaminants such as algae, chloramines and bacteria are destroyed.

However, did you know that a pool that smells strongly of pool chlorine doesn’t mean that it’s clean? In fact, a clean pool will be almost odor-free. As The Home Depot puts it, “Strong chlorine smell is a sign of improperly treated water. The odor actually comes from chloramines, also known as combined chlorine. Chloramines form when the chlorine in the pool mixes with the nitrogen in sweat, oils and urine. However, smell alone does not dictate when you should shock your pool.”

Know Your Pool Shocking Chemicals and Which One is Right for Your Pool

Don’t feel intimidated if you don’t have a degree in chemistry! There are three main types of pool shocking chemicals: calcium hypochlorite, sodium dichlor and potassium monopersulfate. Here is a breakdown of each.

Calcium Hypochlorite Also known as cal hypo, calcium hypochlorite is the most affordable pool shock. You can get it in 65% and 73% strength, a pH level of 12, and is not stabilized. It provides excellent water clarity while destroying contaminants in pool and spa water, such as those found in sweat, urine and windblown debris. Aqua magazine provides a comprehensive description, instructions for use and cautions.

Sodium Dichlor Also known as dichlor, sodium dichlor is a stabilized pool shock with cyanuric acid for sun protection. You get it in 56% strength with an almost neutral pH level. It does not add calcium to your pool.

Potassium Monopersulfate Also known as non-chlorine shock, potassium monopersulfate oxidizes pool water in a chlorine-free formula that remains unaffected by sunlight, leaves no residue and adds only oxygen. 

Potassium monopersulfate is a strong oxidizer, and has the same oxidation potential as chlorine. There are numerous reasons people use this chemical to shock their pool – such as those who want to avoid chlorine.

Chlorine combines with swimmer and other organic wastes (nitrogen-based compounds) to form chloramines. These by-products are unpleasant and have a foul odor. Potassium monopersulfate also reacts with nitrogen-based compounds, but they don’t form chloramines because it does not contain chlorine.

One noteworthy advantage of shocking with potassium monopersulfate is that you can reenter the pool after a half-hour of adding the chemical – as opposed to waiting 24 to 48 hours before swimming if you shock it with chlorine. Also, the chemical dissolves quickly, and doesn’t fade pool liners. By the way, it also plays well with chlorine and allows it to work more effectively as a sanitizer.

However, there are some disadvantages of using potassium monopersulfate. When it oxidizes urea and chloramines, nitrate ions are the primary oxidation product. Keep in mind that algae feed on nitrate. It can also lower the pH and total alkalinity of your pool. Moreover, this chemical is expensive. It is also crucial to know that the shock dose of 1 lb. per 10,000 gallons of water offer only 1/3 of the oxidizing power of 1 lb. of 65% calcium hypochlorite. And although this chemical is a strong oxidant, it is not a sanitizer – and therefore provides no protection against bacteria and viruses.

As for which type of shock is right for your pool, our blog post – “The Shocking Truth About Shocking Your Pool” – offers the following:

“You can use cal hypo to shock most pools. But if you have hard water and calcium hardness levels are high, you should use sodium dichlor or non-chlorine shock. Every pound of cal hypo adds 5-7 ppm to calcium hardness levels. It is better to use non-chlorine shock for vinyl pools because it doesn’t fade the liners or cloudy the water, and you don’t get a dusty residue. If your pool has increasing cyanuric acid levels, you should avoid dichlor shock because every pound adds some amount of cyanuric acid.”

If you’re a new pool owner, there are some terms you may have encountered that you’re not quite certain about. Here’s a handy list of definitions:

  • Free Chlorine (FC): The amount of chlorine actively disinfecting the water. Proper free chlorine levels are between 1 and 3 ppm.
  • Combined Chlorine (CC): The chlorine that’s been used. It will still be in the water but has a lower sanitizing power. Keep the CC level to less than 0.2 ppm.
  • Total Chlorine (TC) is the sum of FC and CC in your pool.
  • Breakpoint Chlorination: When there’s enough FC to shatter the molecular bonds of chloramine. Once breakpoint chlorination has been reached, the free chlorine in your pool water can begin to build up. Free chlorine does the heavy lifting when it comes to sanitizing a pool.

When and How to Shock Your Pool

The basic rule of thumb is to shock your pool once a week. However, the more often you use the pool, the more frequently you need to shock it. Also shock your pool after any of the following:

  • Heavy pool use, like a pool party.
  • A severe rainstorm – which, of course, includes tropical storms and hurricanes.
  • Major water level change.
  • There has been feces in the pool.

Again, the goal of shocking your pool is to raise the free chlorine level of the pool water to roughly 10 times the combined chlorine level. Reaching this mark is the breakpoint chlorination. You need to reach breakpoint chlorination every time you shock your pool. Not hitting the breakpoint can result in even more chloramines in your pool.

Shocking a pool should be done at dusk. The sun will burn off unstabilized chlorine. Shocking your pool at night ensures the chemicals work properly.

The Home Depot offers the following instructions:

  • Test the water. You will need to check the pH level in your pool. Pool test kits can measure the FC and TC of your water. To find the CC of your pool, subtract the FC from the TC. This will let you know how much chlorine you need to add to the pool.
  • Calculate the amount of shock you will need to mix. Refer to the amount indicated on the package of the shock chemical you plan to use.
  • You can add some granular pool shock to your swimming pool directly, but most varieties need to be mixed with water before use. Mix the granular pool shock with water ahead of time, if necessary. This will save you time and help prevent calculation mistakes. Pre-mix the pool shock in a five-gallon bucket. If using liquid pool shock, follow label instructions.
  • Ensure the pool pump is running.
  • Pour the mixture into the water, around the edges of the pool.
  • Let the pump run for about six hours or more.
  • Test the water to ensure proper chlorine levels.
  • Don’t use the pool right away. Wait for the free chlorine levels to drop to 1 to 3 ppm.
  • Wear gloves and safety glasses while working with pool chemicals.

The Take-Home Message

Shocking your pool can keep your pool water safe and clean. If we’ve provided you with information on how to do that more effectively, we’re glad! But when it comes to pool maintenance, there is another issue that you need to watch out for: pool leaks.

Finding a leak in your swimming pool can be a difficult job. Some leaks are easy to locate, but there are many that pool owners can’t detect without professional assistance. Certified Leak Detection uses technology and techniques we have developed over 20 years in business. In addition to quick detection and repair of swimming pool leaks, we provide industry-leading leak detection and repair for spas and hot tubs, as well as slabs and foundations. Serving areas throughout Central Florida – including Orlando, Longwood, Lake Mary, Sanford, Kissimmee, Clermont and Winter Springs – our team is ready to answer your call.

Contact us for quick, reliable service.


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