Pool Shocking: What Is It & Why Does Your Pool Need It?

We’re moving headlong into the dog days of summer, and few things bring such immediate relief as a dip in the pool. If you’re lucky enough to have a pool in your own backyard, you know that a host of day-to-day maintenance tasks are essential to keep the water safe and inviting. This guide will focus on one such task in particular: shocking your pool to keep algae, bacteria, and other contaminants at bay.

What is Pool Shocking?

Shocking a pool or hot tub refers to the temporary increase of chlorine or other chemicals to clean the water. Over time, various contaminants build up or proliferate in pool water, even when the water is chemically treated. This can lead to cloudy or discolored water, or even water that is unsafe to swim in. Shocking the water periodically keeps these contaminants in check.

The pool shocking process can take some time because the chemicals need to thoroughly circulate throughout the water. Pool shocking chemicals can also irritate your skin and eyes, so it’s important to wait anywhere from 8 to 24 hours before swimming. Always test your pool water after shocking to confirm that the chemical and pH levels are within acceptable ranges.

Why Pool Shocking Is Essential

You might wonder why shocking a pool is so important when the water is already treated with chlorine or other chemical cleaners. Everyday baseline chlorine levels strike a balance between the capacity to disinfect and a person’s chemical tolerance. In other words, chlorine levels can’t be too high, otherwise the water would damage our skin and eyes. So, we set chlorine levels somewhere between 1.0 and 3.0 parts per million (ppm),which is high enough to keep the water clean for several days or even a few weeks, but not so high that harmful contaminants can’t gradually build up. 

Here is what shocking a pool helps to combat:

• Algae Growth

Algae are photosynthetic organisms that thrive in aquatic environments. Standing bodies of water—like a backyard pool—are prime spaces for algae to colonize.

Some types of algae produce toxins that are dangerous—even lethal—for people and animals to touch or ingest. Fortunately, shocking a pool can kill off algae before a bloom can develop.

Important to note is that algal blooms are often worsened by fertilizers and storm runoff. We’ll mention more on pool shocking frequency later on, but know that it is important to shock your pool after a significant summer rainstorm for this reason.

• Bacteria

An inadequately maintained pool can also be the perfect environment for various kinds of bacteria, which may be introduced by bathers, animals, or the surrounding environment. Some types of bacteria can make us quite sick. Of particular concern are cyanobacteria, which are often confused with algae and produce blue-green toxic blooms on the water’s surface. Regular shocking keeps bacteria populations from getting out of hand.

• Chloramines

Chloramines are chemical compounds formed when chlorine combines with ammonia or amines. Chloramines can function as disinfectants and are sometimes used to disinfect drinking water, but you don’t want an abundance of chloramines in your pool for a couple reasons. First, chloramines are not as effective at disinfecting water as free chlorine is. Second, chloramines can make for an unpleasant swimming experience because they irritate our eyes, skin, and even respiratory systems. That familiar “chlorine smell” around swimming pools actually comes from chloramines rather than chlorine itself.

Amines in pools typically come from a bather’s perspiration, saliva, or urine. The amines bind with the free chlorine to form chloramines, or combined chlorine, lowering the levels of free chlorine in the water. Shocking the pool resets this balance. 

• Cloudy or Murky Water

A common pool problem that most pool owners are bound to encounter is cloudy or hazy water. Poor water clarity can have a number of possible causes, from inadequate filters to malfunctioning mechanical equipment, but the accretion of chloramines and other compounds is a common culprit. Shocking your pool every so often is critical to maintaining clear water.

Types of Pool Shock Treatments

There isn’t just one way to disinfect a pool. In fact, there are several options for pool owners to investigate.

• Liquid Chlorine

One common way to disinfect a pool is to simply add a large dose of liquid chlorine to the water. Note that this will increase free chlorine levels and help to kill off microorganisms, but liquid chlorine is not the same thing as chemical pool shock.

• Calcium Hypochlorite

Calcium hypochlorite, or cal hypo, a chlorine-based shock treatment, has been the standard for disinfecting pools for nearly a hundred years. It’s simple, powerful, effective, and inexpensive.

Note that you need to dissolve calcium hypochlorite shock prior to adding it to your pool, and some owners may find that this shock treatment leaves a white residue of calcium on the pool floor.

• Lithium Hypochlorite

Lithium hypochlorite is another chlorine-based shock treatment. Many people find it superior to calcium hypochlorite, particularly because it dissolves more quickly and can be added directly to the pool with no predissolving required. It’s also less likely to leave behind residue and is ideal for pools with hard water.

The downside? Lithium hypochlorite is pricier than other shock treatments. It also may be hard to find. Some manufacturers have discontinued production of lithium hypochlorite because of the limited availability of lithium.

• Sodium Dichlor

Sodium dichlor—or just dichlor–is notable because it is safe to use as a shock treatment for saltwater pools. Dichlor also shares the advantage of lithium hypochlorite of dissolving quickly. This means it is usually okay to add dichlor directly to the pool.

• Non-Chlorine Shock

Not at all shock treatments use chlorine as an active ingredient. Using chlorine-free shock is a safe and effective way to reduce chloramine levels, oxidize oils and grime, and improve water clarity in both saltwater and traditional pools. It’s also fast. Water may be suitable for swimming in as little as 15 minutes.

There is one caveat. Non-chlorine shock will not kill bacteria, viruses, or algae. If you need to thoroughly disinfect your pool or kill off an algal bloom, a chlorine-based shock treatment is typically required.

Step-by-Step Pool Shocking Guide

Shocking your pool should be a standard part of your pool maintenance during the summer. Follow these step-by-step pool shocking instructions.

1. Test your pool’s water.

Start by testing the water to ensure pH and alkalinity levels are in the optimal ranges. The pH level should be between 7.4 and 7.6. Alkalinity levels should be between 100 and 150 ppm.

2. Put on protective equipment.

If you’re using a chlorine-based shock, take precautionary measures to avoid burns and eye irritation. Wear long rubber gloves and safety goggles. Long pants and long sleeves are also advisable to protect your skin from splashes. Make sure you’re wearing old clothes, though. The chemicals in pool shock can stain.

3. Determine the appropriate amount of shock and predissolve as needed.

Refer to your product’s packaging to determine how much shock to use. The general guideline is one pound of shock per 10,000 gallons of pool water.

 If you’re using calcium hypochlorite or another pool shock that requires predissolving, fill a large bucket about three-quarters full with warm water. Add the shock about a pound at a time and carefully stir until dissolved.

4. Start your pool’s pump.

Don’t forget to get your pool’s pump up and running. The continual circulation of the treated water throughout the pool’s system is essential.

 5. Pour the shock into the pool.

Now you can start to add the shock to the pool. Pour gently to avoid splashback. Work your way gradually around the pool’s perimeter instead of pouring solely in one place.

6. Allow the pump to circulate water for several hours.

With the shock in the pool, you can now clean up. If you’re using a chlorine-based shock, keep the pump running for six to eight hours, or however long the shock manufacturer recommends.

7. Retest the water.

After at least six hours, retest the water to confirm the pH, alkalinity, and chlorine levels are in acceptable ranges. Avoid swimming until you’re sure that the free chlorine levels are between 1.0 and 3.0 ppm.

Best Practices for Pool Shocking

We’ll end with a few more helpful tips:

• Shock your pool in the late afternoon or evening. UV rays from the sun can degrade chlorine, rendering a chlorine-based shock less effective.
• Don’t mix pool shocks. There’s no need to turn your pool into a science experiment. Mixing pool chemicals can produce volatile and dangerous compounds.
• Be mindful of when shocking is necessary. You don’t need to shock your pool every day. It’s wise to do so when you open your pool for the season. We also advise shocking your pool after a heavy rainstorm or pool rainstorm. Otherwise, your pool use should dictate how often you shock the water. Once every two weeks is a good rule of thumb.

And, of course, there’s much more to pool maintenance than routine shocking. You’ll also need to attend to the filters, pumps, and other mechanical components, and a home warranty can help you keep your equipment in great shape.