Three Types of Pool Shock: What's the Difference?

Whether you’re a new pool owner or experienced pool professional, it's important to understand the difference between the three main types of pool shock: dichlor, cal-hypo, and chlorine-free. Each of these types of shock has a different purpose in maintaining a clean, safe, and well-sanitized pool.

Before we explain the different types of pool shock, let’s go over the main reasons shocking is needed. Shock is used when chlorine levels are low, chloramine levels are high, algae is present, or if there's been a fecal accident in the water. Shocking is also beneficial after heavy pool use or a major weather event, including heavy rains or high winds, which can bring extra dirt and debris into the water.

Below, you can compare the different types of shock and the issues they address. This will help you figure out which one is right for your pool and when it's best to use it.

Calcium Hypochlorite Pool Shock: Power Powder Plus 73

Leslie's Power Powder Plus 73, a powerful calcium hypochlorite shock, is our most popular chlorine pool shock, and for good reason: it effectively gets the job done so you can return to the water faster. Leslie's Power Powder Plus 73 is the fastest dissolving granular shock on the market. This particular cal-hypo pool shock is 73% calcium hypochlorite, which means it can handle the toughest algae and bacteria problems. Rescuing your pool from an algae bloom or major contamination is a snap with Power Powder Plus 73; it gives you the highest dose of available chlorine available. If you plan to use cal-hypo shock all season long, we recommend purchasing the 25-pound buckets, which will save you time and money over the individual 1-pound bags.

Leslie's Power Powder Plus 73 Pool Shock Features

• A powerful and effective form of pool chlorine
• 73% calcium hypochlorite with 70% available chlorine content
• Quickly kills bacteria, and controls algae and other contaminants
• Can be used in saltwater pools
• Great for pools with normal-to-low pH
• Ideal for all pool surfaces

Things to Keep in Mind with Cal-Hypo Pool Shock

• It may briefly cloud pool water depending on water conditions, including high pH levels or warm water temperatures.
• Cal-hypo has a high pH of 10.8–11.8, which will raise the pH of your pool.
• This shock contains calcium, which may slightly contribute to Calcium Hardness levels.
• Cal-hypo is an unstabilized form of chlorine, meaning it doesn't contain Cyanuric Acid.
• Don't pre-mix cal-hypo before adding to the pool. Broadcast it directly over the pool surface, and disperse settled granules with a pool brush.
• Always follow the label directions. Use, handle, and store with caution in a cool, dry, well-ventilated area.
• Don't allow swimming until Free Available Chlorine levels return to 2.0–4.0 ppm.

Cal-Hypo Shock Dosage

Adding 9-18 ounces of Leslie's Power Powder Plus 73 per 10,000 gallons of pool water will provide 5–10 ppm Free Available Chlorine to superchlorinate the pool. We recommend testing sanitizer levels at least 2–3 times per week, depending on Cyanuric Acid levels, pool usage, and weather conditions.

Dichlor Pool Shock: Chlor Brite

Leslie's Chlor Brite (sodium dichloro-s-triazinetrione) is ideal for saltwater pools and pools with vinyl liners, fiberglass, or other sensitive surfaces, since it's a fast-dissolving pool shock. It's also great for use in spas and hot tubs. If high pH and/or Calcium Hardness levels are a concern, then this is the shock of choice. Dichlor is a stabilized chlorine that contains Cyanuric Acid (CYA), so it’s perfect if your pool has low CYA, or if you use unstabilized chlorine as the primary sanitizer in your outdoor pool. In addition to routine weekly shock treatments, Chlor Brite can also be used for daily applications to maintain a chlorine residual.

Leslie's Chlor Brite Pool Shock Features

• Fast-dissolving shock with 55% available chlorine content
• pH level of 6.0–7.0 (near neutral)
• Perfect for all types of pools
• Won’t cloud the pool water
• Dissolves quickly for a fast chlorine boost
• Can be broadcast directly onto the water surface

Things to Keep in Mind with Dichlor Pool Shock

• Dichlor contains Cyanuric Acid, which will increase residual CYA in the pool over time.
• We don't recommend using this type of shock if you're already using another type of stabilized chlorine, such as 3" trichlor tablets. Otherwise, you'll increase your CYA levels even faster.
• Monitor CYA levels closely during swimming season with regular weekly water tests.
• Don't allow swimming until Free Available Chlorine levels return to 2.0–4.0 ppm.
• Always read and follow product label instructions for usage and storage.

Dichlor Shock Dosage

Adding 16 ounces (1 pound) of Leslie's Chlor Brite per 10,000 gallons of water will increase your Free Available Chlorine level by 6.8 ppm. As with other types of shock, we recommend testing sanitizer levels at least 2–3 times per week, or more often depending on water quality scenarios.

PRO TIP: To make sure you're getting the most out of the chlorine products for your pool or spa, check out our post on How to Maximize Chlorine Efficiency in Your Pool.

Chlorine-Free Pool Shock: Fresh 'N Clear

Leslie's Fresh ‘N Clear is a powerful chlorine-free pool oxidizer, safe for all pool surfaces. Since chlorine-free shock doesn't contain chlorine, it must be used in conjunction with a water sanitizer like chlorine, bromine, or a saltwater chlorine generator. We encourage hot tub owners to add a small dose of Fresh 'N Clear after every use to quickly oxidize contaminants. Both indoor and outdoor pools can also benefit from chlorine-free shock. The fast-dissolving formula works quickly to oxidize non-living organic contaminants in the water, reducing chloramine formation and freeing up your chlorine to work more effectively. When using Fresh 'N Clear, the water is safe for swimming in just 15 minutes. In addition, there are no harmful byproducts produced by non-chlorine shock, making it great for long-term use without adverse chemistry impacts.

Leslie's Fresh 'N Clear Pool Shock Features

• Oxidizes contaminants quickly
• Reduces and prevents inorganic chloramines
• Reactivates bromine
• Able to swim within 15 minutes
• Reduces itchy skin and eye irritation
• Won't bleach swimsuits or vinyl pool liners
• Improves chlorine efficiency if used weekly, saving money
• Neutral pH of about 7.4, which won't impact pH levels
• Improves water clarity and complements enzyme treatments
• Ideal for all pool and spa surfaces
• Easy application; broadcast across pool surface

Things to Keep in Mind with Chlorine-Free Pool Shock

• Chlorine-free shock will not kill germs or algae.
• This product will not change chlorine levels. Only use this product if your Free Available Chlorine or Free Available Bromine levels are within the ideal range. For chlorine pools, this is means FAC levels are between 2.0–4.0 ppm.
• As with all pool chemicals, always read and follow label directions for usage and storage. However, this product is generally safe to use.

Chlorine-Free Shock Dosage

For initial treatment, to reach breakthrough oxidation, use Fresh 'N Clear at a rate of 2 pounds per 10,000 gallons of water. Afterwards, most residential pools will require a weekly application of 1 pound per 10,000 gallons. For pools that get used more often and have a large amount of non-living organic contaminants, more frequent applications are recommended.

Shock Weekly for Best Results

To maintain a clean, safe, and beautiful pool, sanitize the water daily with an automatic chlorine feeder or floating chlorine dispenser to maintain a chlorine residual. Then, shock the pool at least once per week to oxidize contaminants, boost Free Available Chlorine levels, and control germs and algae in the pool. If you have questions about maintaining proper chlorine levels in your pool or choosing the right type of shock, call or stop by your local Leslie's to speak with one of our friendly pool experts. Bring a water sample while you're at it, and we'll check your water chemistry for free with our in-store AccuBlue® 10-point water analysis.