To swim in clean, clear, pleasant-appearing water in your backyard pool, you need to make pool shock treatments part of your pool maintenance routine. This step ensures that your pool has the right balance of chemicals to keep contaminants from overtaking your water while eliminating chloramines: chemicals created when ammonia is added to chlorine.
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.
HTH Pool Care Shock Advanced Pool Care Shock Advanced
1 pound treats up to 13,500 gallons
Use in a variety of pool types
Doesn't contribute to CYA levels
Granules may settle on pool floor
Can promote calcium hardness
Keep your water safe and swim-ready with the help of HTH Pool Care Shock Advanced. This popular pool shock treatment uses calcium hypochlorite (cal-hypo), a bleaching agent and disinfectant. Depending on your water chemistry, we recommend this pool shock because it can be used in chlorine, saltwater, and bromine pools, and it contributes to clear water while eliminating chloramines, bacteria, and algae.
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
Type: Granule | Amount: 12 pounds | Chlorine level: Not applicable | Dissolve time: 24 hours
Champion Pool Shock
Ready-to-use; no mixing
Doesn't promote scale or CYA
Can pour directly into pool water
Results in bleach stains if spilled
May need repeating
Liquid chlorine is a simple and economical way to shock your pool. If you go this route, we recommend Champion Pool Shock. It is ready-to-use, meaning you don’t have to do any poolside mixing before treating your water. You have your choice of pouring it directly in the pool or distributing it through a dosing pool pump.
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
Type: Liquid | Amount: 4 gallons | Chlorine Level: 12.5 percent | Dissolve Time: Not applicable
EcoOne OneShock Spa & Swimming Pool Tablets
Easy-to-handle small tablets
Also used in spas and hot tubs
Alternatives cost less
The convenience of using a pre-measured tablet is hard to beat, so you may want to consider a similar option to shock your pool. We recommend EcoOne OneShock Spa & Swimming Pool Tablets, which are convenient to use and dissolve quickly.
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
Type: Tablet | Amount: 2 pounds | Chlorine Level: 55.5 percent | Dissolve Time: Not applicable
Best for Algae
Clorox Pool & Spa XtraBlue Shock
Targets various pool algae
Can re-enter water in 15 minutes
Treats 12,000 gallons per pound
May require reapplication
May raise CYA levels
An algae bloom is one reason why you may need to use pool shock, since pool algae can grow quickly, leaving a furry trail of green, black, or yellow slime on the surface of your pool steps or in the corners—basically anywhere water circulation may be more limited. Clorox Pool & Spa XtraBlue Shock is an effective and popular treatment option that targets common algae species while eliminating bacteria and chloramines. Since this pool shock uses a stabilized form of chlorine, it may increase CYA levels.
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
Type: Granule | Amount: 12 pounds | Chlorine Level: 39 percent | Dissolve Time: 15 minutes
Best Cal-hypo Shock
DryTec Calcium Hypochlorite Chlorine Shock Treatment
Lacks cyanuric acid
Fights algae, organic contaminants
Can bleach surfaces
Calcium can cloud water
Calcium hypochlorite is often used as an active ingredient in pool shock formulas. Most commonly referred to as cal-hypo shock, it’s a popular pick because of its ease of use and affordability. DryTec Shock Treatment is a great option to consider if you want a granular pool shock. Plus, it contains no stabilizer, so it shouldn't contribute to a buildup of cyanuric acid, which can render the chlorine in your swimming pool ineffective.
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
Type: Granule | Amount: 24 pounds | Chlorine Level: 65 percent | Dissolve Time: Not applicable
In The Swim Sodium Di-Chlor Chlorine Granular Pool Shock
Near 100 percent sodium di-chlor
Can be used in spas
Contains no calcium
Can elevate CYA levels
May need to use a pool brush
We like sodium di-chlor products because generally, they are easy to use, dissolve fast, and don't alter the pH balance of your pool. We recommend In the Swim Sodium Di-Chlor product because it contains 99 percent sodium di-chlor, with 56 percent available chlorine. Also, this product contains no calcium, avoiding cloudy water, as well as unsightly buildup on pool surfaces. We have noted that this product is as effective on above-ground pools as in-ground pools, and also can be used with spas and even fountains. The manufacturer says 1 pound of product effectively treats 10,000 gallons of pool water. Or use 2 pounds if applying as an algicide until the algae are all dead and vacuumed out.
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
Type: Granule | Amount: 28 pounds | Chlorine Level: 56 percent | Dissolve Time: Not listed
Clorox Pool & Spa Salt Pool Shock Oxidizer
Can be used in saltwater or bromine pools
May cause false high chlorine readings
Doesn’t kill algae or bacteria
A non-chlorine shock uses enzymes to eliminate contaminants such as sunscreen, oils, makeup, fertilizer, and more. For a chlorine-free option we recommend Clorox Pool & Spa Salt Pool Shock Oxidizer. This formula can be used in saltwater and bromine-treated pools and works fast—you can enter the water in as little as 15 minutes. Keep in mind that non-chlorine pool shock formulas don’t kill living organisms, so it’s not effective against algae or bacteria.
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
Type: Granule | Amount: 6 pounds | Chlorine Level: Not applicable | Dissolve Time: 15 minutes
Best for Above-ground Pools
In The Swim Di-Zap Multi-Shock
Eliminates chloramines & algae
May be applied in direct sun
Can raise CYA levels
Besides introducing unsightly blemishing, bleaching can sock the resins out of an above-ground pool's vinyl liner, walls and floor. The fast-dissolving granules of Di-Zap Multi-Shock, by pool supplier In The Swim, are less likely to bleach or erode your vinyl liner. In most cases, granules dissolve in about an hour. The formula also can act as a shock, algaecide, and chlorine stabilizer.
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
Type: Granule | Amount: 24 pounds | Chlorine Level: Not listed | Dissolve Time: 1 hour
Our best overall pick is HTH Pool Care Shock Advanced, which you can use in most types of pools and doesn't raise CYA levels. It's a granule formula that is also easy to apply, though you may need to use a brush to fully dissolve the product. For a very simple and economical option, you can also use liquid chlorine; we recommend Champion Pool Shock. It can be poured directly into your water or distributed through the pool pump, but be careful not to splash it on your clothes.
What to Look For in a Pool Shock
Pool shock treatments are categorized by type: liquid, powder, and granule. Which type you choose depend on your objective, and importantly, frequency of water treatment. "There are some shocking solutions that are intended for weekly maintenance, and some that are specific for contaminated water or to treat algae blooms," says Phil O'Haver, a pool expert at Leslie's Pool Supply, a national chain of consumer pool and spa care products. "It can be more complicated to treat an incorrectly shocked pool than the original issue, so ensuring you use the correct one is imperative."
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.
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.
What type of pool shock do you need?
The condition of your pool water may change based on the proximity of vegetation, amount of sunlight the pool receives, and, especially regarding above-ground pools, age, which can cause the vinyl in your liner and other components to break down. Based on your pool's condition, you may opt for a stabilized, unstabilized, or chlorine-free option. If you have elevated CYA levels, choose an unstabilized shock to avoid chlorine lock. If you have elevated calcium hardness, then you should avoid cal-hypo shock. Saltwater or bromine pool owners may opt for a chlorine-free shock treatment, although separate treatment solutions are needed to fight algae or bacteria growth. You should always test your pool water in conjunction with pool shock treatments to ensure that you're maintaining the right balance of chemicals.
How often should you apply pool shock?
The frequency of using pool shock depends on environmental and usage factors. O'Haver offers these general guidelines: "You should shock your pool during pool opening and closing season, as well as during storms, algae outbreaks, or when using your pool a significant amount in a small period of time." For some pool owners, a weekly shock may be necessary; others may find that it's required less often, and most notably at the beginning and end of the pool season.
Why Trust The Spruce?
This article was written by Erica Puisis, a freelance writer and product tester for The Spruce. Puisis 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 the national chain of consumer pool and spa care products Leslie's Pool Supply, for insights on how to select the best shock for your pool. O'Haver also answered common questions about how to choose pool shock and the best times to apply it.