Everything to Know About Pool Shocking

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When you own a pool, sanitizing and shocking it are part of the deal. Here at Zagers, we get lots of questions about both: how shocking and sanitizing are similar/different, when to do either, what products to use… the list goes on and on. 

To help, we’ve put together this post to answer the most common questions about sanitizing and shocking your pool, so you and your family can safely enjoy it all summer long. 

What is Pool Shock?

Pool shock is basically super chlorinating your pool to kill all the nasties and the chloramines in it. 

You may be asking chlora-what? Chloramines, which is also known as combined chlorine. Let us explain.

When you add chlorine to your water, it’s known as “free chlorine,” because it’s free to work hard and disinfect your pool. When you and others swim in your pool, contaminants like sweat, make-up, oils, and other unpleasantries attach themselves to the free chlorine. 

The result is called “combined chlorine,” or chloramines, because the chlorine isn’t “free” to do its work anymore – instead, it’s combined with those other elements, which you can think of as weighing down the “free chlorine” and keeping it from doing its job. 

The “total chlorine” in your pool is simply the combination of those two: it’s the sum of how much “free chlorine” and “combined chlorine” is in your pool.

When your pool has too many chloramines, it’s time to shock it! When you shock your pool, you’re adding a super dose of chlorine to kill the chloramines, essentially splitting the combined chlorine and releasing the free chlorine so it can get back to work.

When Should You Shock Your Pool?

We recommend shocking your pool once a week as part of regular maintenance to help prevent algae, raise your chlorine level and kill contaminants. In addition to your weekly maintenance, there are six more common instances when you should shock your pool:

1. Start of the season. Doing so ensures that you’ll start with fresh, clean water, as it will kill algae and anything else that’s grown since you closed it.

2. After lots of use. One of the wonderful things about owning a pool is sharing it with others. But when you have multiple swimmers, the number of contaminants increases, as well. This problem is easily solved by shocking and lets everyone get back to fun in the sun quickly.

3. After a storm. Wind and rain can alter your pool’s pH levels and add all sorts of unwanted debris to your pool. If the rain has added significant water to your pool, be sure to lower the water level to normal before shocking, so you’re not unnecessarily needing to use extra shock (to compensate for the additional water).

4. After several sunny, warm days. After a West Michigan winter, we anticipate the return of summer and poolside time with friends and family. Ironically, sunshine can break down the chlorine that keeps your water clean. Using pool shock after a stretch of sunny days eliminates the chloramines and other organisms that can grow with the sun.

5. When your free chlorine is outside the ideal range. As you probably know, the Center for Disease Control recommends (and we agree!) that you should keep your pool’s free chlorine levels at 1-3 parts per million (ppm). If it falls below that range…gross! Low levels of chlorine encourage the growth of bacteria, algae and more. When levels of chlorine are above 3 ppm, your water can be very acidic, potentially damaging your pool as well as causing nose, eye, and skin irritation.

6. End of the season. When it’s time to close your pool for the season, give it one last shock. Doing so will help keep it cleaner while closed and make opening your pool next year that much easier. (You’ll still want to shock it again when you open it.)

Types of Pool Shock

Hopefully, that helps clarify what shocking your pool is, as well as why and when you should do it. Now let’s talk about some products you can use to shock your pool. A couple of common terms to know are stabilized and unstabilized chlorine (or shock), and non-chlorine shock. You may also hear about liquid and granular shock – liquid is exactly that, a liquid chlorine product and granular simply means that the chlorine is in powdered form. 

Stabilized Chlorine

Stabilized chlorine has cyanuric acid added to the chlorine, which prevents the UV rays from the sun from quickly burning off your pool’s chlorine, making it last longer — sort of like sunscreen for your chlorine. They often come in sticks and tablets for daily sanitizing but it is also available in one type of shock, Sodium Dichlor. It comes in granular form and dissolves quickly. If you like the convenience of being able to shock your pool at any time of day, we recommend BioGuard Smart Shock. Not only does it contain algaestats, clarifiers, and optimizers, but it allows you to swim in just 15 minutes! It is our most popular pool shock option.

Unstabilized Chlorine

Unstabilized chlorine does not have cyanuric acid added, which means it burns off more quickly than stabilized chlorine. For daily sanitization, this product tends to work best with outdoor pools that are in a lot of shade or indoor pools. 

Unstabilized chlorine can be ideal for shocking your pool because the high concentration spikes the level of chlorine, killing the chloramines and gives your pool that crystal clear, clean look. A few common types of unstabilized chlorine are:

1. Cal Hypo. The technical name of this pool shock is Calcium Hypochlorite. It’s widely used because it’s effective and affordable . It typically comes in granular form. Zagers carries BioGuard Burnout 73 that has the highest percentage of Cal Hypo (73% as the name suggests). Other brands typically contain 56%, and therefore, are less effective. 

2. Sodium Hypo. Officially known as Sodium Hypochlorite, or regular old liquid bleach. It Is important to note that the bleach you use around the house has a very low percentage of Sodium Hypo and is not recommended. You’ll want to use a brand that is made for pools. The big distinction is that it will be called “Liquid Chlorine” and the Sodium Hypo content will be at least 10%. One benefit of Sodium Hypo is that it’s non-scaling, so it doesn’t leave any residue on your pool.

Keep in mind that if you use unstabilized chlorine to sanitize your pool, you may want to pair it with cyanuric acid to provide stabilization and slow the effects of the UV rays on the chlorine. BioGuard Stabilizer 100 is a great option for this application.

Non-Chlorine Shock

Called Potassium Peroxymonosulfate, non-chlorine shock goes to work on those nasty chloramines in your pool. It also dissolves quickly, doesn’t fade vinyl liners, and works quite well with indoor pools. For those looking for this option, we carry BioGuard OxySheen. 

Because of its different composition, however, non-chlorine shock can leave more nitrates in the water, which are great food for algae—not something you want breeding in your pool. As such, you may still want to use chlorine sanitizers at times to kill unwanted bacteria and algae. In addition, non-chlorine shock tends to be a pricier option than the others.

Time Your Shocking Right

In terms of timing during the day, you can use stabilized shock any time since it has UV protection. As we mentioned before, BioGuard Smart Shock allows you to swim in as little as 15 minutes afterwards (be sure to follow the manufacturer’s directions).

Unstabilized shock should be used in the evening, after sundown, because UV rays can break down the chlorine and it needs time to work. 

In addition, we suggest that:

  • You don’t use any type of shock on a windy day. If you do, more shock could get blown around than makes it into your pool!
  • You leave your pool cover off and don’t put it back on until chlorine levels have returned to normal.
  • You always test your water after shocking to make sure it’s balanced.

Now that we’ve covered the basics of when to shock your pool and what types of shock are available, let’s get down to the nitty, gritty of how to shock your pool.

How to Shock a Pool: Step-by-Step 

1. Do your prep work. Before you begin, uncover your pool, skim it, and brush and vacuum the walls and floor.

2. Make sure you have protective gear. You’ll want to wear protective goggles, gloves, and clothes you can work in (nothing nice!).

3. Prepare the chemicals. It’s imperative that you follow the manufacturer’s directions based on the type of shock you’re using and the size of your pool.

4. Add the shock. Follow the manufacturer’s directions and let it work for the time specified. If you’re using a granular product, be sure to brush off any product that spills on your pool deck.

5. Run your pump and filter. It’s preferable that you run them continuously for 24-48 hours but, at a minimum, follow the manufacturer’s directions.

6. Test your water. As we mentioned above, you’ll always want to test the water after you shock your pool. To do so, use a clean plastic container, scoop about 1 qt. of pool water from elbow-depth, and check your chlorine levels, including pH, total alkalinity and calcium hardness. When the levels are correct, swimming can resume! Until then, it’s safest to keep everyone out of the pool. If you’re a Zagers’ customer, bring your water sample in once a month and we’ll test it for free!

7. Maintain your pool. As we mentioned earlier, in addition to shocking your pool in the specific situations we addressed, it’s a good idea to shock it weekly for maintenance. We realize this is a lot of information, but wanted to be sure you understand both the reasons it’s important to shock and sanitize your pool, the chemicals you can shock and sanitize with, as well as how to shock your pool. If you’d like to talk to an expert to find out more, or have questions, please don’t hesitate to contact us. We’re always happy to help.

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