It doesn’t matter whether you’re a new pool owner or an old hand, shocking your swimming pool might seem a little scary. That’s okay—handling such a high volume of chemicals can make anyone feel jittery. It gets easier with practice and knowledge. Once you learn what pool shock is, understand why it’s one of the most important chemicals to use, and learn how to shock a pool, the whole process will start to feel pretty routine. That’s good, because shocking your pool on a regular basis is a simple way to prevent stray algae and bacteria from taking root in your water. It also helps keep your pool smelling … well, hopefully like nothing at all. What Is Pool Shock, Anyway? Think back to the last time you walked past a hotel pool. The chemical smell probably knocked your socks off, right? You may think that unmistakable smell is chlorine, but the odor actually comes from chloramines, a sign of improperly balanced water. Chloramines form when the chlorine in your pool mixes with the nitrogen in sweat, oils, and urine (which we’re sure isn’t in your water, though we can’t vouch for the hotel). This is a natural chemical process, basically a byproduct of your chlorine doing its job. In addition to giving your pool a funky smell, too many chloramines can also irritate your skin, eyes, and respiratory system. By shocking your pool, you’re adding enough chlorine (or other chemical) to clean the water and destroy the buildup of chloramines. This process is also called superchlorination. Pool Chlorine 101 Before we dive into how to shock a pool, you first have to understand the difference between total and free chlorine, and what combined chlorine and breakpoint chlorination are. Free Chlorine (FC) is the amount of chlorine actively disinfecting your water. You want your water’s FC level to be between 1 and 3 parts per million (ppm) so the chemical can do its job. Combined Chlorine (CC) is the chlorine that’s been used. It’s still in the water, but its sanitizing power is greatly diminished. You want to keep your CC level at less than 0.2 ppm. Total Chlorine (TC) is the sum of FC and CC in your pool. Pool water testing kits can measure the FC and TC of your water. To find the CC of your pool, simply subtract the FC from your TC. Breakpoint Chlorination is when you have enough FC to shatter the molecular bonds of chloramine. You need to add ten times the amount of CC to hit this point. Try to reach the breakpoint every time you shock your pool. Not hitting the breakpoint can result in even more chloramines in your pool, and if the chloramine levels continue to rise unchecked, you may eventually have to partially or even fully replace your water to fix the issue. Types of Swimming Pool Shock You generally can’t shock your pool using your regular chlorine tablets, but you do have your choice of products when it comes to pumping up your chlorine levels. Calcium Hypochlorite Also known as cal hypo, this chemical has been used to disinfect swimming pools and municipal water sources since 1928. It’s one of the most inexpensive and convenient ways to shock your pool. Features Most commercial versions contain between 65% and 75% chlorine. Calcium hypochlorite needs to be dissolved before you add it to your pool. It must be used after dusk. It will be roughly eight hours before you can safely swim again. It adds about 0.8 ppm of calcium to your water for every ppm of FC added, so use caution if your water source already has a high level of calcium. Lithium Hypochlorite If your water has high calcium content, and you don’t mind paying a little extra, lithium hypochlorite is the way to go. It dissolves much more quickly than calcium hypochlorite, so you can add it directly to your pool without dissolving it beforehand. Features Commercial versions contain 35% chlorine. It must be used after dusk. It will be roughly eight hours before you can safely swim again. It can be toxic to aquatic life (making it a solid algaecide), so you must take care when disposing of recently treated water. Note: You may have a difficult time finding lithium hypochlorite. Some pool chemical manufacturers have stopped producing it due to the rising cost of lithium, most of which is now used to make lithium batteries. Dichlor The actual names of this swimming pool shock chlorine are sodium dichloro-s-triazinetrione or dichloroisocyanuric acid. (Try saying either of those five times fast.) Dichlor shock is much easier to say and even easier to use. Depending on the brand, you may be able to add it directly to your pool. Features It typically contains between 50% and 60% chlorine. You can use it for both regular chlorine doses and shock treatments. You typically don’t have to dissolve it ahead of time. It adds 0.9 ppm of cyanuric acid for every ppm of additional FC. It must be used after dusk. It will be roughly eight hours before you can safely swim again. Non-Chlorine Shock If you’re looking to shock your pool and take a dip soon afterward, this is exactly what you need. Non-chlorine shock using potassium peroxymonosulfate is a fast, inexpensive pool shock alternative. Features You can add it directly to your pool water at any time. It will be roughly 15 minutes before you can safely swim again. Because it doesn’t rely on chlorine, it does not function as an algaecide. When to Shock Your Pool You might have noticed the instructions on chlorine shocks say they need to be used after the sun has gone down. This is because the sun will burn off unstabilized chlorine, which means the shock won’t be as effective. Shocking your pool at night makes sure the chemicals work the way they were meant to. How Often to Shock Your Pool You don’t want to wait for a bad smell or itchy eyes to happen before you shock your pool. We recommend shocking your pool once a week, or at least once every other week to properly maintain your water chemistry. The more often you use the pool, the more often you should reach for the swimming pool shock. In addition to your weekly or semi-weekly treatments, you may want to perform an extra pool shock under certain circumstances, such as after: heavy pool use (like a pool party) a severe rainstorm or damaging winds (especially if your pool collected debris) a major water level change a bowel-related pool accident Think of extra shocks as insurance against wayward algae and other contaminants. It’s better to take out any bacteria before it has a chance to affect the quality of your water or make anyone sick. How to Shock a Pool You’ve got the chemical knowledge. Now it’s time for practical experience. Superchlorinating your pool is shockingly (sorry, we couldn’t resist) easy once you get the hang of it. Important: Remember, if you’re using chlorinated pool shock, wait until the sun goes down before adding it. Supplies Protective eyewear Chemical-resistant gloves Pants and long-sleeved shirt (that you won’t mind messing up) Closed-toe shoes Water test strips or liquid testing kit Shock of your choice 5-gallon bucket (if you need to dissolve the pool shock before adding it to the water) Wooden stick (for stirring to dissolve)