Chloramines are essential to keeping your drinking water potable, “but can produce an unpleasant smell that is irritating to your eyes and nose,” says Phil O’Haver, a pool expert at Leslie’s Pool Supply, a national chain of consumer pool and spa care products, with whom we consulted for this article. “Pool shock works to destroy contaminants in the water and break down these chloramines.“Besides consulting with O’Haver, we researched all types of pool shock, keeping in mind that different pool and maintenance routines call for different forms. Our top pick is HTH Pool Care Shock Advanced. This cal-hypo shock treatment can be used in most types of swimming pools. Also, it doesn’t raise cyanuric acid levels, which helps eliminate concerns over the condition known as chlorine lock, when the chlorine in your pool becomes ineffective. Here are our top pool shock treatments. This formula is free of cyanuric acid (CYA), which can cause chlorine lock. However, you need to monitor your water for calcium hardness, which, in elevated levels, can cause scale on your pool wall, steps, and water features. Dosing and applying HTH Pool Care Shock Advanced is simple, since each 1-pound pouch of granules treats 13,500 gallons of water. You should use a pool brush to fully dissolve any granules that settle at the bottom of the pool. The dissolve time can take up to 24 hours, but testing your pool’s water chemistry is the easiest way to know when it’s safe to swim again.Price at time of publish: $58 This liquid pool shock has 12.5 percent of sodium hypochlorite (a form of chlorine) for maintaining your pool water or closing it at the end of the season. It shouldn’t cause cloudy water when used according to the manufacturer’s instructions, and it also shouldn’t cause a buildup of scale or CYA. Before you uncap this liquid pool shock, keep in mind that the liquid can bleach your clothes or other surfaces if you accidentally spill it. Some people avoid liquid pool shock for this reason, but it’s very affordable and readily available if you don’t mind taking extra precautions. Price at time of publish: $60 This shock tablet can be used for in-ground or above-ground swimming pools, along with spas and hot tubs. The tablets are small and require minimal handling, and the number of tablets you use is based on how many gallons of water you treat. The product label suggests two tablets for every 1,000 gallons of water, which may mean you need to buy this pool shock in bulk for larger pools. This pool shock formula is highly concentrated, with 99 percent sodium dichloro-s-triazinetrione (most often referred to as sodium dichlor), a common sanitizer and algaecide. However, using this provides CYA, which in high levels may result in pool lock. EcoOne touts how well this product dissolves, which means you shouldn’t have to worry about gritty residue settling on the pool floor. You pay for this convenience and effectiveness, with these shock tablets being one of the pricier treatments we researched. However, it’s a worthwhile option to consider if you want super-simple maintenance for your pool or hot tub. Price at time of publish: $50 This granule pool shock, with algae-fighting crystals, specifically addresses some of the most prevalent types of pool algae such as black, green, and mustard algae varieties. The formula requires 1 pound of product for every 12,000 gallons, which means it stretches a little farther than some other pool shocks that only treat 10,000 gallons per pound of formula. You can re-enter the pool in as little as 15 minutes following standard shock treatment, after ensuring the chlorine level is 1 to 4 parts per million. However, for algae treatment, you need to let the product work for as long as 24 hours, then reapply it 72 hours later in cases of stubborn growth. Be prepared to roll up your sleeves as well, since the manufacturer recommends that prior to application, you brush pool surfaces that have algae growth while the pool filter and pump are running. Price at time of publish: $92 To use DryTec pool shock, you need a 1-pound pouch for every 10,000 gallons of water. Since this is a chlorine shock treatment, you also need to dissolve the product in a bucket of water before adding it to your pool water, and ensure that the pool pump is running. The granules can be slow to fully dissolve, so you may need to use a brush to scrub the pool floor to keep the product from settling and causing discoloration, especially on vinyl, fiberglass, or painted pool surfaces. Price at time of publish: $100 We have noted that this product’s price point compares favorably with other sodium di-chlor products, and also can be used in saltwater pools. Since this is a granule product, we recommend that you apply the product while your filter pump runs. You may need a pool brush to disperse granules that have not dissolved. Also, this product contains cyanuric acid, which can nullify chlorine’s effectiveness at too-high levels. Price at time of publish: $210 Whether it’s for a pool or spa, this chlorine-free shock should be distributed in the deepest part of the swimming area, with the pump running. Since it lacks unstabilized chlorine, you can apply it regardless of sun exposure, although the manufacturer recommends morning or evening application. As a “shock and swim” treatment, you don’t have to wait hours to resume swimming. However, be aware that this product may cause false high total chlorine readings for up to 72 hours. Price at time of publish: $68 This 3-in-1 shock formula comes pre-packaged in 1-pound pouches that treat 10,000 gallons of water each. It relies on 99 percent sodium dichloride to eliminate combined chlorine, which can cause skin irritation and odor. It also targets algae growth. You can use Di-Zap Multi-Shock in sunny conditions, since it contains stabilizer to prevent the degradation of chlorine from the sun’s rays. The tradeoff is that this pool shock can elevate CYA levels, so you need to keep a close eye on your pool’s water chemistry. Price at time of publish: $155 Liquid pool shock treatments rely on chlorine, usually in the form of sodium hypochlorite, poured directly into your pool water. It’s an economical and easy option, but it risks staining your clothes or other surfaces if the product splashes or spills. For this reason, many people choose powder or granule pool shock treatments. Usually, powder pool shock requires you to measure out the appropriate amount, based on the size of your pool; minimize contact with your skin. Granules are similar, but generally are pre-packaged into 1-pound pouches. Follow the dosing recommendations to determine how many pouches of product you need to effectively shock your pool. Keep in mind that with this type of pool shock, you may need to use a pool brush to scrub undissolved granules that settle on the pool floor.
Chlorine Content
The amount of available or free chlorine is often specified, as a percentage, on the packaging of pool shock treatments. This tells you how much chlorine is available to eliminate organic waste and keep your pool clean and clear. Pool shock treatments for routine maintenance may contain 55 percent or so free chlorine, while stronger super shock treatments may have as much as 70 percent. Non-chlorine shock treatments don’t directly raise free chlorine levels in your pool. However, by using enzymes to destroy organic matter in the pool water, they free up the existing chlorine to target bacteria and algae more efficiently.
Stabilized vs. Unstabilized
On its own, chlorine is subject to rapid breakdown when exposed to ultraviolet rays, such as in sunlight. To keep the chlorine present and available to sanitize your water, some pool shock treatments are stabilized against chlorine loss with cyanuric acid (CYA). However, when CYA levels become too high, a condition known as “chlorine lock” can occur. This means the chlorine present is over-stabilized and rendered ineffective for sanitizing.
Why Trust The Spruce?
This article was written by Erica Puisis, a freelance writer and product tester for The Spruce. Erica has researched many aspects of pool care and maintenance, including pool cleaners and water testing kits. As she evaluated pool shock treatments, she took into account the various needs of different pool types, as well as the treatment objectives a homeowner may be looking for. Products were evaluated on factors such as type, ease of use and application, dissolve time, and overall cost. While researching the different types of pool shock treatments, she spoke with Phil O’Haver, a Pool Expert with Leslie’s Pool Supply, for insights on how to select the best shock for your pool. Phil also answered common questions about how to choose pool shock and the best times to apply it.
