The Best Chlorine Tablets for Fighting Algae and Cloudy Water

Chlorine tablets offer a convenient way to maintain a sanitary swimming pool by steadily releasing chlorine that kills bacteria and helps prevent algae growth. To find the most reliable options, we tested five chlorine tablets and one tablet dispenser for 2 months in a new Florida pool, monitoring water clarity, chlorine stability, dissolving rate, ease of use, and algae control.

Unlike liquid chlorine, pool chlorine tablets are premeasured and dissolve gradually in a floating dispenser, skimmer basket, or automatic feeder. This makes them particularly convenient for routine maintenance, though pool owners still need to regularly test the water and keep free chlorine between 1 and 3 parts per million and pH between 7.2 and 7.8. Stabilized tablets can also gradually increase cyanuric acid levels with prolonged use.

Our top pick is the Clorox Pool & Spa Active99 because they maintained clear water and steady chlorine levels while remaining straightforward to handle and store. The individually wrapped tablets reduced chlorine odors inside the storage bin, and their standard 3-inch size fit easily into common floating dispensers.

Ahead, learn what to consider when comparing tablet sizes, formulas, dissolving rates, and packaging, and see which tested options earned a place among the best chlorine tablets.

1. BEST OVERALL: Clorox Pool&Spa Active99 3-Inch Chlorinating Tablets
   ↓ Jump to Review
2. RUNNER-UP: Rx Clear 1-Inch Stabilized Chlorine Tablets
   ↓ Jump to Review
3. BEST BANG FOR THE BUCK: In The Swim 3-Inch Stabilized Chlorine Tablets
   ↓ Jump to Review
4. BEST WITH ALGAECIDE: Clorox Pool&Spa XtraBlue Chlorinating Tablets 
   ↓ Jump to Review
5. BEST FOR SALTWATER POOLS: HTH 42055 Pool Care 3-Inch Chlorine Tablet
   ↓ Jump to Review
6. BEST TABLET DISPENSER: 440 Pool Chlorine Floater Dispenser
   ↓ Jump to Review

Chlorine Tablets Comparison

Our Top Picks

A pool vacuum and filtration system can’t do all the work to keep pool water clean and clear. Based on our testing, the top choices in this list represent some of the best chlorine tablets on the market that balance the chemical composition of pool water.

Our Ratings

This 35-pound bucket of individually wrapped Clorox chlorine tablets is a reliable option for pools that see regular use throughout the swimming season. During 2 months of testing in a Florida pool, the tablets maintained clear water and steady chlorine levels without requiring frequent adjustments. Each 3-inch tablet treats up to 5,000 gallons of water, though regular water testing is still necessary to maintain the proper chlorine balance.

The tablets dissolved slowly and consistently in a floating dispenser, and their standard 3-inch size fit easily into common floaters and automatic feeders. The individual wrappers were especially convenient, making the tablets easier to handle while helping contain the strong chlorine odor inside the storage bucket. Considering the quantity included, the large bucket also offers reasonable value for routine pool maintenance.

These trichlor tablets contain cyanuric acid, which helps protect chlorine from breaking down rapidly in direct sunlight. That stabilization was useful in the intense Florida sun, but prolonged use gradually raised the pool’s cyanuric acid level. Pool owners should test the water regularly and occasionally supplement or alternate with unstabilized chlorine when needed.

What our tester says: “Clorox is dominant in the pool chlorine industry for a reason. These tablets gave me a crystal clear pool, plus the individually wrapped tablets keep the chlorine smell out of my garage.”—Paul Rankin, Product Reviews tester and writer

Get the Clorox Active99 chlorine tablets at Amazon.

Our Ratings

These 1-inch trichlor tablets from Rx Clear are particularly useful for smaller pools, spas, and compact automatic feeders. During testing in a Florida pool, their smaller size made it easier to fine-tune the chlorine dosage than with standard 3-inch tablets. The stabilized formula also helped the chlorine resist rapid breakdown in strong sunlight, which made the tablets well suited to hot, sunny conditions.

The tablets dissolved slowly and could be used in a skimmer or automatic dispenser. However, larger pools may require several tablets at once to maintain the proper chlorine level, making them less convenient than a single 3-inch tablet. Some tablets also arrived chipped or broken, leaving small pieces and residue at the bottom of the bucket. Those fragments can still be used, but they are messier to handle and harder to dose precisely.

As with other stabilized trichlor products, regular water testing remains important because continued use can gradually increase cyanuric acid levels.

What our tester says: “These smaller 1-inch tablets gave me a little more control over how much chlorine I put in my pool at once, which helps fine-tune the water chemistry a little more easily.”—Paul Rankin, Product Reviews tester and writer

Get the Rx Clear chlorine tablets at Amazon.

Our Ratings

This 50-pound bucket from In The Swim offers strong value for pool owners who expect to use chlorine tablets throughout the swimming season. It contains approximately 80 individually wrapped 3-inch tablets, and during testing, the formula consistently maintained clear, sanitized water. The wrappers were easy to open and helped keep chlorine odors, dust, and broken fragments contained inside the bucket.

Each tablet treats about 5,000 gallons of water and dissolves gradually when used in a floating or automatic chlorine dispenser. The large quantity makes this one of the most economical options over time, although the oversized bucket carries a higher upfront cost and can be heavy to move or store.

These trichlor tablets are stabilized with cyanuric acid, which helps slow chlorine loss in direct sunlight. That makes them useful for sunny pools, but continued use can gradually raise the pool’s stabilizer level. Regular water testing is still necessary, and the tablets should not be treated as a completely hands-off maintenance solution.

Get the In the Swim chlorine tablets at Amazon or Leslie’s Pools.

Our Ratings

Algae can quickly turn clear pool water cloudy or green, especially during hot, humid weather. During testing in a Florida pool, the Clorox Pool & Spa XtraBlue tablets provided excellent algae control while maintaining noticeably clear water. The 3-inch tablets combine chlorination and algae prevention in a single formula, reducing the need to add separate products for routine maintenance.

The tablets dissolved slowly and released chlorine consistently when used in a floating dispenser. Clorox states that the formula helps prevent scale, corrosion, and stains while controlling green, mustard, and black algae. It also contains stabilizer to help protect chlorine from rapid breakdown in direct sunlight.

These tablets cost more than several standard trichlor options, but their multipurpose formula may justify the premium for pools that frequently struggle with algae. The bucket lid was also quite difficult to open, which made routine refilling less convenient.

Get the Clorox XtraBlue chlorine tablets at Amazon or Lowe’s.

Our Ratings

Pool owners looking to stretch the time between tablet refills may appreciate the HTH 42055 Pool Care 3-inch chlorine tablets. During testing, the slow-dissolving tablets provided close to a week of consistent performance while maintaining stable chlorine levels, clearer water, and noticeably less algae.

The multipurpose formula combines a sanitizer, clarifier, and algaecide, helping address several routine pool-maintenance needs with a single tablet. The tablets can be used in a floater, feeder, or skimmer basket and are compatible with saltwater and vinyl-lined pools. They also produced less of a noticeable chlorine odor than some of the other tablets tested.

HTH recommends using three tablets per 10,000 gallons of water, though dosage should always be adjusted according to regular water testing. The large bucket offers plenty of product for ongoing maintenance, but it is quite heavy and can be cumbersome to move or store.

Get the HTH 42055 chlorine tablets at Amazon or Ace Hardware.

Our Ratings

The 440 Pool Chlorine Floater Dispenser is a simple, inexpensive way to distribute chlorine tablets without relying on a skimmer basket or automatic feeder. During testing, it was easy to fill, close, and place in the pool, and its large interior held up to five 3-inch tablets at once. That extra capacity reduced how often it needed to be refilled.

Adjustable vents around the base make it possible to control how quickly chlorinated water flows out of the dispenser. The settings were straightforward to change, making it easier to fine-tune chlorine output based on pool size, weather, and usage. Its bright color also made it easy to spot and retrieve from the water.

The trade-off is build quality. The thin plastic feels inexpensive, and the lid occasionally loosened or popped off while in use. It also has a basic, utilitarian appearance that may not appeal to pool owners who want less visible equipment. Although it performs well for the price, it may need to be replaced once or twice a year if handled roughly or left exposed to harsh sunlight.

Get the 440 chlorine tablet dispenser at Amazon.

Jump to Our Top Picks

How We Tested the Best Chlorine Tablets

To choose the best chlorine tablets, we considered products from leading pool-care brands before testing five tablet formulas and one floating dispenser for 2 months in a new Florida pool. The tablets included both 1-inch and 3-inch options, along with standard and multipurpose trichlor formulas. We evaluated how steadily each product maintained chlorine levels, how effectively it kept the water clear, its algae control, dissolving rate, ease of dosing, tablet condition, packaging, odor containment, value, and compatibility with common floaters and feeders. We also monitored whether prolonged use contributed to rising cyanuric acid levels. 

The dispenser was assessed for tablet capacity, ease of filling, adjustability, chlorine distribution, lid security, and overall durability. Each pick was selected according to its strongest real-world performance, such as overall reliability, value, algae prevention, longevity, or suitability for smaller pools.

Our Testing Scores

What to Consider When Choosing Chlorine Tablets

When selecting chlorine tablets, note several factors, including the type, size, and dissolving speed of the tablet, as well as the appropriate amount of pool chlorine for the size of the pool along with a few key safety tips. Keep reading to learn more about choosing the best chlorine tabs to balance the chemical composition of pool water.

Stabilized vs. Unstabilized Chlorine

Stabilized chlorine contains cyanuric acid, which protects chlorine from rapid breakdown caused by sunlight. Most trichlor and dichlor products are stabilized, making them useful for outdoor pools in hot, sunny climates (like our test pool in Florida). Because the chlorine remains active longer, stabilized tablets can reduce how frequently you need to add sanitizer.

However, cyanuric acid accumulates in the water over time. If the level becomes too high, it can reduce chlorine’s effectiveness even when test strips show an adequate chlorine reading. As such, regular water testing and occasional dilution may be needed.

Unstabilized chlorine, including calcium hypochlorite and liquid sodium hypochlorite, does not add cyanuric acid. It is useful when stabilizer levels are already elevated, but sunlight breaks it down more quickly. Many pool owners alternate stabilized tablets with unstabilized chlorine to maintain a balanced cyanuric acid level.

Chlorine Strength

Users can select from several different types of chlorine treatments for a swimming pool or spa, including sodium hypochlorite, lithium hypochlorite, calcium hypochlorite, dichlor, and trichlor. Trichlor is the most commonly used treatment. 

• Trichlor is the most common chlorine treatment for swimming pools. Containing up to 90 percent chlorine, solid trichlor chlorine tablets are a form of stabilized chlorine. Once a tablet dissolves in the pool water, the treatment resists degradation under direct sunlight and UV light, slowing the production of chloramines.
• Sodium hypochlorite is a good option if the pool’s water filtration system struggles with high calcium hardness. However, it contains only about 10 to 12 percent chlorine, so it isn’t the most effective at killing algae or bacteria. Moreover, sodium hypochlorite chlorine treatments are nonstabilized, which means they are vulnerable to degradation in sunlight and can produce harmful chloramines that cause red, itchy eyes and skin irritation.
• Lithium hypochlorite has a higher range of 28 to 35 percent chlorine, which allows it to maintain the chemical balance of the pool water more effectively. However, lithium hypochlorite is not stabilized and is vulnerable to UV radiation.
• Calcium hypochlorite is another nonstabilized pool treatment. While more effective than both sodium hypochlorite and lithium hypochlorite and with a chlorine percentage of about 65, calcium hypochlorite is still vulnerable to UV radiation and chloramine production.
• Dichlor chlorine treatment is combined with cyanuric acid to create a stabilized chlorine treatment that’s resistant to UV radiation and slows the breakdown of chlorine molecules and the release of chloramines into the pool. Dichlor products are typically granular instead of solid tablets, and their chlorine content ranges from 56 to 62 percent.

Tablet Size 

Chlorine tablets usually come in two sizes: 1-inch small tablets and larger 3-inch tablets.

• 1-inch chlorine tablets are a good option for small pools, hot tubs, and spas, because they release a small amount of chlorine at a quick-dissolving speed, rapidly increasing the chlorine level to the correct concentration. However, these tablets are ineffective in larger pools that hold more than 5,000 gallons of water.
• 3-inch chlorine tablets are ideal for large pools because one tablet can treat about 5,000 gallons of water, on average. Pools with more than 5,000 gallons of water can use more than one chlorine tablet, though the dissolving time is much slower for 3-inch tablets.

Both sizes can be used in skimmers, floating chlorine dispensers, and automatic chlorine dispensers, so choose the right type based on the size of the pool.

Dissolving Speed 

The dissolving speed of a chlorine tablet can be difficult to determine based on product information alone. Factors like application method, water temperature, water pressure, and the size of the tablet can impact the amount of time the tablet takes to break down.

The 3-inch chlorine tablets break down at a slower rate than 1-inch chlorine tablets, while tablets placed in the skimmer rely on a continuous water flow through the filtration system to break them down. Floating dispensers gradually dissolve tablets, but the dissolving speed is unreliable because they simply bump and bob throughout a pool with inconsistent water flow. Automatic dispensers typically have a set rate that will dissolve a chlorine tablet within 2 to 5 hours depending on the size, though users can adjust these devices to increase or decrease the dissolving speed.

Amount and Pool Size

The amount of chlorine required differs for pools, hot tubs, and spas. First, test the water with a pool test kit to determine the pH and chlorine level in the water. Ideally, the pH level should fall between 7.2 and 7.8, while the chlorine level should range between 1 and 3 ppm for the water to be considered safe.

On average, one 3-inch chlorine tablet can treat between 5,000 and 10,000 gallons of water, depending on the manufacturer. However, a single 1-inch chlorine tablet can treat only about 350 gallons of water. If the tablets are chipped or broken, users may need to estimate the treatment based on weight by using 1 pound of chlorine tablets per 10,000 gallons of water.

Safety and Storage

Adding chlorine tablets to a pool is relatively easy with a skimmer, an automatic tablet dispenser, or a floating-tablet-dispenser system. Most chlorine tablets are packaged in a large bucket or container, but many manufacturers also produce individually wrapped tablets to help prevent them from breaking, cracking, and crumbling in transit.

Chlorine tablets can emit a strong odor that’s dangerous in enclosed spaces, so always close and store the container properly. Moreover, use gloves to avoid directly touching the tablets: The high chlorine level can irritate the skin.

FAQs

Along with pool pumps and filters, chlorine tablets are necessary to maintain most swimming pools. However, not everyone knows how they work or how to use them. For answers to these concerns and more, take a look at some of the most frequently asked questions about chlorine tablets.

Q. Can chlorine tablets be used for household cleaning? 

No, experts don’t recommend using chlorine tablets for household cleaning because they contain a high amount of chlorine, which can damage toilets, sinks, and appliances. The chlorine can also cause strong odors in enclosed spaces that are harmful if inhaled in large amounts.

Q. How do I add chlorine tablets to my pool? 

You can add chlorine tablets to the pool in several ways. Use a floating chlorine dispenser that holds the tablet in a basket until it’s fully dissolved. Place the tablet in a pool skimmer where the water will be pulled over it, quickly and efficiently adding chlorine to the pool water. Finally, load an automatic chlorine dispenser with a tablet and set it for a specific chlorine level. The dispenser gradually releases the chlorine into the pool.

Q. How often should I add chlorine tablets to my pool? 

The specific number of chlorine tablets to add per week depends on the size of the pool and the size of the tablets. However, you can use a pool test kit to help maintain a 1 to 3 ppm chlorine concentration in the pool water. You’ll also need to test for the appropriate pH level, keeping it between 7.2 and 7.8 to ensure safe swimming water.

Q. Should I use 1-inch or 3-inch chlorine tablets?

Use 1-inch tablets for spas and small pools; 3-inch tablets are more convenient for larger pools.

Q. What happens if you put too many chlorine tablets in the pool?

Too many tablets can raise chlorine excessively, causing irritation, equipment damage, faded liners, and unbalanced water chemistry.

Q. How long do chlorine tablets take to work?

They begin dissolving immediately, but may take several hours or days to fully release their chlorine.

Q. Can chlorine tablets damage a pool?

Yes. Direct contact with pool surfaces or excessive chlorine levels can bleach liners, corrode equipment, and damage finishes.

Meet the Tester

Product tester Paul Rankin evaluates pool-care products in his Florida backyard, focusing on straightforward, practical insights about performance, usability, and value.

Additional research provided by Timothy Dale

 

All You Need to Care for Your Lawn & Garden

Keeping your grass green and your plants thriving doesn’t just take a green thumb—it starts with the right tools and supplies.

SEE OUR FAVORITES