Let me guess. Since chlorine is a household name, you already know that it’s probably the most popular sanitizer for pools—and really works. And it’s true: this superpowered sanitizer enters bacteria molecules and destroys them from the inside out, keeping pools both sparkling and safe. But when it actually comes to ordering chlorine for yours, you might be surprised to see so many different long, chemical names. Sheesh.
Plus, each chlorine type on the market comes with different tags: liquid, granules, tablets, stable, unstable. Without knowing what each of these terms mean, you could quickly find yourself overpaying for chlorine, or with the wrong kind entirely. I’ll explain why your type of chlorine matters, the difference between stabilized and unstabilized chlorine, and a brief on each type of prominent chlorine on the market—so that you can save time and money, and get the perfect sanitizer for your situation.
Chlorine is Chlorine, Right?
Actually, no. I know, you’ve probably heard the word chlorine countless of times. But it’s actually a blanket term for about five different chemical compounds: dichlor, trichlor, sodium hypochlorite, lithium hypochlorite, and calcium hypochlorite. And these compounds come in different forms, at different price points, and even differ when it comes to whether or not the sun renders them totally ineffective.
Don’t worry, all types of chlorine work to keep your pool clean. But hey, that’s only if you choose the right type for your pool. So unless you like swimming with a ton of bacteria, some of which has the potential to make you sick, and spending an unnecessary amount of money on ineffective sanitizer, you’ll want to read on.
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Stabilized Vs. Unstabilized Chlorine
There are two major types of chlorine: stabilized and unstabilized, and you don’t have to wear a lab coat to work for this detail to matter for you. In fact, understanding the difference between the two is the first step to finding the right chlorine for you. And what does it all come down to? One chemical that might otherwise easily be overlooked: cyanuric acid.
Stabilized chlorine, in addition to its own sanitizing compound, also contains cyanuric acid. This chemical allows chlorine to work at slightly higher temperatures, and ensures that this type of chlorine can work in sunlight. Without cyanuric acid, the sun’s rays would stop chlorine from doing its job.
Unstabilized chlorine is great and all, but it lacks cyanuric acid. And since it doesn’t have that chemical protecting it from the sun, it only works for indoor pools, where direct sunlight isn’t an issue. This is also why types of unstabilized chlorine are never recommended to sanitize hot tubs.
Cyanuric Acid: To Do or Not To Do?
Cyanuric acid sounds amazing, right? Well, it is. But like all good things, you can have too much of it. Every time you add stabilized chlorine to your pool, you increase your cyanuric acid levels. Once these get too high, it’ll stop your chlorine from working at all—which is exactly what we’re not going for. My advice? If you have an indoor pool, get an unstabilized chlorine, even though you could technically use a stabilized type.
Have an outdoor pool but not loving the idea of cyanuric acid taking over? You could always use an unstabilized chlorine and add the cyanuric acid yourself. This way, you have more control over how much is entering your pool, and can even base what you add on your current cyanuric acid levels already present in the water. The magic number for this one is 100 ppm or less.
Stabilized: Dichlor and Trichlor
Congratulations, you’re in the majority. And though it must be pretty sweet to have an indoor pool, as an outdoor pool owner you have access to the most commonly-used chlorine types, which are usually pretty affordable and easy to use. Just make sure that if you use dichlor or trichlor, you also keep tabs on your cyanuric acid level—since it comes in each of these chemical compounds, you’ll have less control over how much is being added to your pool. But hey, that’s one last thing to add to your pool in the short term. And if you’re well-versed on chemical balance, you know it takes an arsenal to keep your pool water clean, comfortable, and safe.
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The Granular Approach: Dichlor
If you’re on the market for a stabilized chlorine that comes in granular form, dichlor (dichloro-s-triazinetrione) is your best bet—and likely your only bet. Luckily, it’s a pretty convenient sanitizer to use. It has a fairly robust concentration of chlorine, between 60-65%, so you won’t need too much of it to get your sanitizer levels up. Plus, it has a pH of 7, which is fairly close to the optimal pool pH level of 7.4-7.6. You’ll probably need some pH increaser, but just a tiny, tiny bit. Plus, granules are easy to dissolve in your pool, unless you like to add sanitizer in a more passive way like I do (putting chlorine tablets in your skimmer while your pump is on couldn’t be easier, in my opinion).
So what’s the fine print? Well, it’s not the cheapest chlorine on the market—though I’d say it’s pretty darn reasonable, considering its chlorine content and the fact that you don’t have to add cyanuric acid separately. Full disclosure: it’s also a fire hazard, so you’ll want to be careful where you store it. And if you’ve got an automated feeder system? Forget about it—this chlorine type dissolves way too fast for that.
The Take-It-From-Me Tablets: Trichlor
This one is my personal favorite for outdoor pools, because these chlorine tablets are both stabilized and super easy to add to your water. And hey, I’m not the only one. Trichlor (trichloro-s-triazinetrione) is super common for residential pools, cost effective, and saves you time. This form of sanitizer also has one of the highest chlorine contents on the market: up to 90%. Just add these white pucks to your skimmer with your circulation system on and let them dissolve evenly across your pool. Now that’s a great feeling.
But like any other sanitizer, trichlor isn’t perfect. It has a low pH of around 3, so you’ll need to use a pH increaser to get your pool between 7.4-7.6. It also doesn’t get along with calcium hypochlorite—meaning it can literally explode when the two chemicals are introduced. It can also lead to metal stains in your pool if its low pH isn’t immediately counteracted.
Unstabilized: Sodium Hypochlorite, Lithium Hypochlorite, Calcium Hypochlorite
Don’t worry, you don’t need to walk on eggshells around these ones. As we’ve covered, “unstabilized” just means that these types of chlorine don’t contain cyanuric acid. Go ahead and add these alone if you have an indoor pool, or in tandem with a separate container of cyanuric acid if you have an outdoor pool. In the end, it’s up to you.
Not for the Faint of pH: Sodium Hypochlorite
Meet “liquid bleach,” which is made up of about 10-12% percent chlorine, salt, and other chemical compounds. Despite its name, this one isn’t for stains on your clothes (or odd colors in your pool, for that matter). And it’s both the most inexpensive of all chlorine sanitizers and common among pool professionals, since it can be added in bulk to larger pools.
So why isn’t it common with residential pools? Well, it naturally has a super alkaline pH—a level of 13 to be exact—and therefore requires a lot of TLC and muriatic acid to keep your pH in check. This, of course, increases the actual cost of using sodium hypochlorite. Another drawback is that liquid bleach can be corrosive to pool surfaces and increases your water’s total dissolved solids (TDS), which might necessitate a partial drain of your pool more often than usual.
If you do decide to go with sodium hypochlorite, be sure you keep it in a cool, dark place—and away from other strong cleaning products. Some people even recommend a secondary containment, which is a system often implemented for hazardous chemicals. Basically, you probably want to keep your container of liquid bleach in a larger, enclosed container. Just in case there’s any, you know, toxic spilling.
Restoring your chemical balance is all the easier with a powerful pump. If a larger horsepower will turn over your water volume at a sufficient rate—and won’t overwhelm your filtration system—then a unit like this Blue Torrent 2 HP Variable-Speed Pump is the one to try. As customer Dave Schmidt says, “My pool has never looked cleaner. I am pleased with my new pump!”
The Niche: Lithium Hypochlorite
Sorry, but lithium doesn’t come cheap. Yes, this is the same material that you can find in batteries, for example—and this is why lithium hypochlorite is the most expensive of these chlorine types. It also has a chlorine concentration of 30-35%, which is better than sodium hypochlorite, and worse than its much, much cheaper cousin, calcium hypochlorite.
So why is lithium hypochlorite still being manufactured and on this list? Well, it’s got a cult following, especially among vinyl pool owners. Since it dissolves super quickly, it is less likely to bleach these pool hypes.
If you’ve got a vinyl pool and you don’t mind spending an extra buck or two to keep it in good shape, then tell your batteries to step aside: you’ve got a bigger lithium player on your turf.
The Prom King: Calcium Hypochlorite
This one is the most popular sanitizer for residential pools, and for good reason: other than liquid bleach, this powder chlorine the most cost effective sanitizer on the market. This is because it has a super-high chlorine concentration of 65-73%, so a little goes a long way. (The rest is calcium chloride, calcium carbonate, and other chemical compounds.) Plus, it also comes in tablet form, which is my recommended method for adding chlorine to your pool. It’s just easier, which you know I’m all about.
So what’s the drawback? Well, there are a couple. First, cal-hypo will raise the calcium hardness levels of your water, and if your water stays too hard for too long, it causes corrosion to your pool’s surfaces. It also has a fairly alkaline pH of about 12. If you decide to go with calcium hypochlorite, you’ll need to keep tabs on both your calcium hardness and pH, and treat your water accordingly.
Oh, and one word of caution: cal hypo is a bit, ahem, touchy. If you put it near some other chemicals, including other types of chlorine, it can spontaneously combust. I’m not kidding. So if this is the type of chlorine for you, you better take extra caution to store it in a safe and, well, isolated space.
A clean pool goes beyond chlorine. Interested in maintaining clean pool floors and walls—without hurting yourself in the process? Try the patented 360-Degree Bristles Black & Decker Pool Brush, developed by long-term pool professionals to eliminate the hip and back pain associated with one-sided brushes.
Hey, You Do You!
We all have to choose our own path in life. You decided to live in this house with this pool, right? (By the way, great decision if I can say so myself.) And now that you’ve learned how to maintain your pool the DIY way, you know that taking care of a pool is all about making a series of calls, all of which could potentially save you time and/or money. And now that you’ve found the right type of chlorine for you, you never have to revisit this choice again. Every pool is unique—take this moment to enjoy yours.