How to Buy Pool Chlorine

Chlorine tablet in water with bubblesChlorine is the most popular sanitizer in America for swimming pools, wells and water treatment.

Swimming pool chlorine is produced in many types, shapes and concentrations; so many that it can get downright confusing, especially if you’re a new pool owner.

This article will discuss chlorine in all its forms, and provide some ways to understand the costs and benefits of the dozen or so different chlorine products we offer at In The Swim.

As a means of differentiation, let’s first break down chlorine into two groups: those types used for everyday chlorination, and types used for pool shocking or super chlorination.

Daily-Use Pool Chlorine Products

To maintain a residual of at least 1.0 ppm (parts per million) in your swimming pool, the best chlorine products are slow-release types that are stabilized, or protected from sunlight degradation. Since they are used everyday, they should be safer to handle and also fairly pH balanced. The higher the percentage of available chlorine, the better – pound for pound, you’ll get more chlorine for your dollar.

Chlorine Tablets & Sticks

3 inch jumbo chlorine-tabletsTrichloro-S-Triazinetrione is the most popular type of chlorine for everyday use. It comes packaged in 3in. tablets, 1in. tablets or as Sticks. Different “pressings”, but chemically the same. Known as “Trichlor” for short, most varieties are 89% available chlorine (although In The Swim’s tablets are 90%).

Sticks or Tablets; no difference other than shape. Some prefer tablets, as they will “stack” better inside of a chlorinator or floater. The large tablets are typically 6 ounces, whereas the sticks are slightly larger at 8 ounces. The 1in. mini-tabs are a bit faster dissolving than the 3in. tabs (sometimes called chlorine pucks, because they resemble a hockey puck), due to their increased surface area exposed to your pool water. Smaller tabs are useful for chlorinating spas or for larger pools that need a faster dissolving tablet.

D.O.T. shipping regulations require that chlorine tablets be individually wrapped. This can be inconvenient when you need to open many of them, although it does reduce the amount of chlorine handling and lowers the chances of contamination from dirt, debris or other pool chemicals.

Trichlor has a low pH value, close to that of Coca-Cola, around 3.0. This can lead to a steady decline in your pool’s pH level, and for some pools, will require adjustment to the pH by occasionally adding a pH increaser.

Trichlor is a stabilized form of chlorine, which means that they have a bit of Cyanuric Acid pressed into the tablet, to shield the chlorine molecule from the sun. You’ll still need to add additional stabilizer (also called conditioner) to maintain a level of 40-60 ppm.

Liquid Chlorine

Liquid chlorine for poolsPrimarily used by large commercial pools that have their chlorine delivered by a truck, into 50 gallon vats. The cost is cheaper than tablets when purchased in such large quantities.

But it’s mostly water, 88% water actually, and 12% available chlorine. Chemically, it’s known as Sodium Hypochlorite, the same composition as Clorox bleach, which has a 5% concentration. Indeed, many industry types refer to liquid chlorine as “bleach”.

Florida pool service guys frequently use bleach on their regular service routes, pouring in a gallon on each visit. Liquid chlorine burns clean, without residue, but using it without a metering pump, so that it can be slowly and consistently introduced to the water has the disadvantage of creating a very high initial chlorine level, followed by a rapid and steady decline.

The pH level of bleach is very high – at 13, it’s almost off the scale. Pools that use liquid chlorine will also need to continually add an acid to decrease the pH level.

Liquid chlorine is not stabilized, and burns off quickly in the bright sun. Those that will use it for everyday chlorination should maintain a level of Cyanuric acid in the pool, in the range of 40-60 ppm.

Granular Chlorine

granular pool chlorineAlso known as “Shock” or chlorine powder, granular chlorine comes in many forms, which I’ll discuss below. It’s great for superchlorination, or shocking the pool, but for use as an everyday chlorination product however, it has limitations.

For one thing, it burns off quickly, even if you use “Dichlor“, the stabilized form of pool shock. That’s precisely what it’s meant to do, dissolve quickly and kill rapidly – but it’s soon depleted. Secondly, some types of granular chlorine leave behind their binders as they dissolve – shock dust, as I call it, all over the floor of the pool. Third, although the fast-dissolving types of granular chlorine allow you to swim immediately, other types will ask you to wait 24 hours before entering the pool, to avoid getting undissolved granules in your eyes.

Finally, using shock chlorine as your primary chlorination product will also deplete your wallet quickly. Pound for pound, it can be the most expensive type of chlorine. Easy to use, but an expensive habit. Not the best choice for everyday pool chlorination.

For everyday residential pool chlorination, buy the strongest available tablets or sticks, at the best price you can find. Some designer brands may wrap their tabs in plastic sleeves, color them blue or claim that their additives are of better quality. Nonsense. Chlorine production is a highly regulated industry, and Trichlor is Trichlor. Compare the label, look at the active ingredients – and save yourself some money.

At In The Swim, we price our chlorine with extremely tight margins because we know that pool owners shop for the best price on chlorine, and when they find it – they usually stick around a while.

Shocking Pool Chlorine Products

Cal-Hypo Pool Shock

InTheSwim pool shockCal Hypo Pool Shock treats 10,000 gallons per pound. It is recommended to first pre-dissolve the shock in a bucket of water before adding it to the pool. This is to avoid bleaching a pool liner, or clouding the water. Cal-Hypo shock is a 68% available calcium hypochlorite, and is a non-stabilized pool shock. It kills fast, but leaves behind a “shock dust”, and overuse can raise your calcium hardness levels as the chlorine separates from the binders.

Super Pool Shock

buy super-pool-shockSuper Pool Shock is a more concentrated form of Cal-Hypo pool shock. It has 5% more available chlorine, at 73% calcium hypochlorite. Cal-Hypo is a non-stabilized shock, containing no cyanuric acid. One pound of Super Pool Shock treats 10,000 gallons. Dilute it in a bucket of water before adding it to the pool; to prevent liner bleaching and cloudy water. Cal Hypo is favored by many due to it’s low cost and ease of use. For best results, lower the pH to 7.2 before shocking the pool.

Chlorine-Free Pool Shock

buy chlorine free pool shock, non chlor shockNon-Chlorine pool shock is chlorine-free but can be used with chlorine or bromine pools. Don’t use Chlorine-Free shock if you use a biguanide system, like Splashes, it will remove some of the biguanide, cloud the pool and accomplish little. Non-Chlor shock burns off dead chlorine and contaminants to increase the free chlorine count in your pool water and can also be used in spas to activate a bromine bank. Advantages of Chlorine free pool shock is that you can swim immediately, it’s pH neutral and there is no shock dust.

Chlorine-Free shock is an oxidizer, but not a sanitizer. Our chlorine-free shock is 43% Potassium Monopersulfate. You may also see non-chlorine shock labeled as Potassium Peroxymonosulfate, same thing. When comparing non-chlor shocks, just like chlorine shocks, check the label for the percentage of active ingredient.

Lithium Pool Shock

buy lithium poolshockLithium pool shock is made of Lithium Hypochlorite. Lithium pool shock can be used with pools in hard water areas. It will not bleach or stain your liner, or cause cloudy water because it dissolves very rapidly. One pound of Lithium pool shock treats 12,000 gallons and is close to a neutral pH. Lithium shock is only 35% available chlorine, but is very fast acting and won’t raise your calcium hardness levels.

Assure Multishock

buy assure multi shockAssure Multishock is a mix of cal-hypo, clarifiers and conditioner. Assure shock is used at a dosage of 1lb per 13,000 gallons, and has become a popular shock with many of our customers. It should be pre-dissolved and you’ll need to wait 8 hours before swimming. Assure is made up of a stabilized form of 47% calcium hypochlorite.

Cloud-Out Pool Shock

cloud out pool shocksCloud-out pool shock was created for biguanide pools, but also works in chlorinated pools. If you use Baquacil, Splashes or Soft Swim in your pool, Cloud Out won’t interfere. It acts as a clarifier and oxidizer and stays active in the water for 7-10 days. Use 2lbs per 12,000 gallons.  Cloud-Out burns clean and removes suspended particles almost instantly. It’s not a chlorine pool shock, like the others here, but it’s worth mentioning. Great for treating cloudy pool water.

Dichlor Pool Shock

Dichlor pool shock is usually sold in buckets, under many trade names. It is the only stabilized form of pool shock, containing some cyanuric acid in the mix. This raises the price of this chemical a bit, but also makes it a good chlorine shock for algae treatments. It has an almost neutral pH level, but otherwise behaves similar to cal-hypo. It typically has a 56% available chlorine level, and is a close cousin to Tri-chlor.

Liquid Chlorine

Liquid chlorine for pools

Liquid chlorine, or bleach, is made of a 12% sodium hypochlorite solution. It can be added at a rate of 2 gallons per 10,000 gallons for the purpose of shocking the pool. It burns clean without residue or “dust”, and seems to have a synergistic effect when added to a pool previously shocked with cal-hypo. It can be hard to find however, and retailers are unable to ship this product, due to D.O.T. restrictions. Can you shock the pool with regular Clorox? Sure you can! You’ll just need more of it, since Clorox is only 5% available chlorine. Just wear your old clothes – bleach does a great job of … bleaching!

A Word on the Safe Use of Chlorine Products

Never, ever mix chlorine products! None of these products mentioned above can be mixed together, and never mix other pool chemicals with chlorine. Explosions and a raging inferno is the result. Always keep chlorine compounds out of the reach of children, stored in a cool, dry location – and keep them separate, so that there’s no chance of accidental mixing of chlorine products.

When opening a bucket of tablets or a bag of shock, always hold your breath. Moisture in buckets can create a strong gas, which is why it’s always best to store tablets in a dry location, not outside in the elements.

When closing a bucket of tablets, always secure the lid tightly to prevent a child from opening the lid, taking a big whiff, and falling face first into the bucket.

When using a bag of chlorine shock, always use the entire bag – don’t store half-used bags of pool shock. This would risk contamination or mixing with other chemicals.

Choose the Best Chlorine for You

There’s a lot to choose from in the world of pool chlorine. Use the product that best meets your needs, and then look for the best price you can find. Compare the percentage of available chlorine, and don’t be fooled by statements like 99% active ingredient, which is different from the % of available chlorine.

If you have questions about which chlorine product to use, or how to use it, feel free to call or send us an email. We love to “Talk Chlorine”!




Brett Rotelli
InTheSwim Staff Blogger


How to Buy Pool Chlorine — 8 Comments

  1. Hello, I usually us a chlorine tab that has 89% tricolor but have found a cheaper brand that has 84.x%. Will this percent difference make a difference or should I continue to use the same product. What is the difference in results between the two percentages? Does it matter. Also other ingredients on the cheaper one is 5.95% vs .7%. Trying to figure out if the difference is worth the cost based on the chemical value. I appreciate any and all feedback.

    • Hi Jayne, Trichlor tablets can range from 84% to 90% Trichlor by pound, the rest is usually made up of binders, but some “Multi-Tabs” also add in other things like clarifiers or alkaline substances, to help raise pH, to counteract the low pH of Trichlor. 5% available Trichlor won’t make much difference in sanitizing the pool, you may not even notice needing to use 5% more tablets… the additional binders, and less expensive binders possibly, does create more ‘gunk’ in the chlorinator as they dissolve, leaving behind an oily, scaly white residue which can clog Off-Line chlorinators especially fast. Otherwise, I usually do advise people to “buy the cheapest chlorine you can find, and the most expensive algaecide”, as a general rule. Try it and see how it works.

  2. I’m confused as to which shock to order for my pool. Why so many choices? I just want to shock it when it’s needed. I use the chlorine tabs .my pools 40,000 gallons . I want to buy the shock in bulk but I’m lost in which to get even after reading this. Please help. I live in S.C. .Not sure if that matters.

    • Hi, there are a lot of pool shock choices, you are correct. There are 3 main types, Cal Hypo, Di-chlor and Non-chlor. Cal Hypo (Pool Shock and Super pool shock) is cheapest and strongest, but is not stabilized from the sun, and adds calcium to the pool. If you have problems with hard water, or have a liner and want to avoid pre-dissolving, you may want to avoid cal hypo. Di-chlor (Di-Zap or chlorine granules) is stabilized with cyanuric acid, and has a more friendly pH level. It’s best for use during the day, because of the addition of the cyanuric acid stabilizer, but for those who have trouble with rising cya levels, you may want to avoid Di-Chlor shock. Non-chlor shock is used by pool owners that want to use less chlorine, or are protecting a vinyl liner from high chlorine levels. Its not as effective on algae or certain types of rare bacteria, but non-chlor is a powerful oxidizer that won’t harm liners and you can swim immediately afterwards. We also have Lithium, for those that have a liner, and want to avoid calcium and stabilizer, and who have a lot of money, cuz it’s the most expensive. For most people, Cal Hypo shock (our Pool Shock and Super Pool Shock) is the best shock to use. So, unless you have some specific needs or demands, that is….

  3. Water in pool turned green due to rain and no chlorine in it.I discovered bleach,is sodium hypochlorite as is chlorine. Because I can buy it for 1 dollar instead of 5 for chlorine at pool store,would it be OK to use that to clear water up?

    • You can use bleach for shocking the pool, yes. Low priced bleach is usually also a low % of chlorine, maybe only 3%. It also may contain impurities. Regular brand name bleach is 5-6%, be sure to use only plain bleach, with no softeners or scents. Pool bleach, or sodium hypochlorite delivered to commercial pools and dry cleaners, or sold in pool stores, is 12.5% available or over twice as strong, but can be hard to find in some areas. For Clorox 5% bleach, use about 5 gallons per 10,000 gallons of pool water, for a heavy shock of 30 ppm, to remove dark algae conditions.

  4. Hi Brett
    I need to talk chlorine. I have a 6500 gallon fiberglass pool with a cartridge filter. I use a chlorine feeder, 1 or 3 inch trichlor tablets. I have a hard time controlling pH, it is always low, and stabilizer builds up quickly to 100 or more. Short of using bleach, how do I prevent these two issues? I use borax to bring up pH to prevent more stable from being added with pH up. What can I do next year? Draining and refilling in June/July not really an option. We are on a well. thank you

    • Hi

      How about installing a nature2 express purifier, so you can reduce your chlorine level to .5, and cut your other problems in half, or by 2/3? Another option would be to use bromine tablets, if you do, you”ll need to install a new brominator. Bleach may be an option, if you have a local source for 5 gallon drums. But with bleach, you”ll still have pH problems, but it will be too high, not too low.

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