Liquid Chlorine vs Chlorine Tablets: Which Is Best?



Wondering if you should be using liquid chlorine or chlorine tablets?

Despite both being viable options when it comes to sanitizing your pool, there are a number of benefits and drawbacks of each that make should be considered. We’ll break it all down in this article.

Quick answer: Liquid chlorine is generally better for your water long-term. Chlorine tablets contain either cyanuric acid or calcium which continue to dissolve and build up in the water, eventually requiring a partial or complete water change.

What is Liquid Chlorine?

Quality Chemical Chloro-Guard Chlorine/Pool Grade Liquid Chlorine / 12.5%...
Quality Chemical Chloro-Guard Chlorine/Pool Grade Liquid Chlorine / 12.5%...

    Liquid chlorine, or sodium hypochlorite as it’s technically called, is a popular type of chlorine used to kill bacteria, algae, and other contaminants in pool water.

    It typically comes in large plastic jugs containing anywhere from 10-12.5% available chlorine. It comes pre-mixed with water and salt, which is then poured directly into the pool without further diluting.

    The liquid itself appears as a yellow-greenish liquid and smells like household bleach — because it basically is a strong bleach.

    Fun fact: Aside from injecting straight chlorine gas into your water, this is one of the purest forms of chlorine you can use.

    Benefits of Using Liquid Chlorine

    These are the pros:

    1. It Doesn’t Contain Cyanuric Acid or Calcium

    Liquid chlorine is a simple mixture of chlorine, water, and salt. Unlike chlorine tablets, it doesn’t contain cyanuric acid (stabilizer) or calcium, so it won’t continue to add these substances to your water.

    While having some cyanuric acid and calcium in your water is beneficial, too much of either substance will eventually lead to scaling and other water issues that can only be fixed by draining and refilling the pool.

    You don’t have to worry about any of that with liquid chlorine, and for many pool owners, this alone is enough to make the switch.

    2. It Gets to Work Immediately

    Liquid chlorine works faster than tablets when added to the water.

    Given its liquid form, it only takes a few minutes to dissolve and disperse throughout your pool, especially if applied near an active return jet.

    Chlorine tablets simply take too long to dissolve in situations where you need to significantly raise the chlorine level in your pool. We’re not just talking hours here, we’re talking days.

    This also makes liquid chlorine an ideal shock treatment when dealing with algae or other serious contaminants, as it can be added in larger amounts to reach shock level quickly.

    3. It Allows for More Precision

    Besides being quick to work, liquid chlorine can be precisely measured and poured to achieve an exact increase in chlorine level.

    This is useful because it allows you to reliably target your ideal free chlorine level using some simple math, whereas you can only rely on a rough estimate using tablets.

    Not only that, chlorine tablets continue to dissolve in the water regardless of how much chlorine is already present, and this process also speeds up under warmer temperatures. Therefore, it’s not uncommon for the water to become over-chlorinated if left unmonitored.

    Another benefit that’s often missed is that liquid chlorine only temporarily raises the pH of water, meaning you don’t have to constantly check and readjust other markers alongside your chlorine. The same can’t be said for tablets.

    Drawbacks of Using Liquid Chlorine

    Here are the cons:

    1. It’s More Hands On

    Using liquid chlorine is a little more labor-intensive than using chlorine tablets.

    The first and most obvious difference is weight. Transporting and handling multiple 1-gallon jugs of liquid chlorine is notably more difficult compared to moving a single tub of hockey puck-like chlorine tablets.

    More importantly, liquid chlorine needs to be added to your water more frequently, even as much as daily in the beginning (until you figure out how quickly your pool consumes chlorine). And yes, this also means more frequent testing.

    Finally, liquid chlorine spills easily, so handling it requires more protective gear such as a mask, safety goggles, and gloves.

    2. It May Need to Be Paired with Stabilizer

    Unlike chlorine tablets, liquid chlorine is an unstabilized form of chlorine, meaning it doesn’t come mixed with a stabilizer (cyanuric acid).

    Stabilizer protects chlorine from the sun’s UV rays, which would otherwise break it down very quickly. If your pool is exposed to direct sunlight, you will need to use cyanuric acid to prolong its effectiveness in your water.

    While this isn’t a dealbreaker for most, it does require buying and managing a separate chemical product that would usually be bundled into your chlorine purchase. Stabilizer also doesn’t degrade in the water, so you’ll hardly need to monitor it once it reaches the optimal level. 

    Conversely, using chlorine tablets over a long duration will continue to add cyanuric acid to the water, eventually leading to “chlorine lock”. (More on that in the next section.)

    3. It Has a Shorter Shelf Life

    Liquid chlorine doesn’t store well compared to other types of chlorine.

    Even when stored correctly, the potency and effectiveness of liquid chlorine decrease by as much as 50% in 3 months, and by the 6-month mark you’ll be left with what is essentially a jug of salty water.

    If that wasn’t bad enough, failing to store it in a cool, dry, well-ventilated area will result in an even shorter timeframe — especially if it’s exposed to direct sunlight, which further accelerates the decomposition of sodium hypochlorite.

    In short, you’ll need to make regular trips to the store if you’re using liquid chlorine, and they’re not exactly easy to transport either.

    What Are Chlorine Tablets?

    In The Swim 3 Inch Stabilized Chlorine Tablets for Sanitizing Swimming...
    In The Swim 3 Inch Stabilized Chlorine Tablets for Sanitizing Swimming...

      Chlorine tablets are the most common type of chlorine for sanitizing residential swimming pools.

      They come in 1-inch or 3-inch sizes and slowly release chlorine as they dissolve in the water. They’re typically added to the pool using floating dispensers or automatic feeders, but some pool owners place them in their skimmer baskets instead.

      While some chlorine tablets use dichlor or calcium hypochlorite as their active ingredient, most contain trichlor at 90% available chlorine.

      Benefits of Using Chlorine Tablets

      These are the pros:

      1. They’re Very Hands Off

      Chlorine tablets dissolve slowly, which means they release chlorine into your water at a steady, constant rate.

      This process allows for a more hands-off approach to pool maintenance as tablets maintain a relatively stable chlorine level depending on pool size, bather load, and environmental factors.

      Chlorine tablets also only need to be refilled on a weekly (or so) basis. If you’re using an automatic feeder, you can potentially go several weeks without intervention — at least in terms of sanitation.

      2. The “Dosage” is Easy to Figure Out

      We put “dosage” in quotes because it’s far from an exact science.

      The general rule of thumb for 3-inch chlorine tablets, which is the most commonly used variant, is to use 1 tablet for every 5,000 gallons of water, per week. This is always rounded up.

      For example, you would use 3 tablets for both a 13,000-gallon and a 15,000-gallon pool, while a 16,000-gallon pool would use 4 tablets.

      This approach is convenient for busy pool owners who don’t have time to constantly monitor their chlorine level or carry out regular testing, though it doesn’t eliminate the need for testing.

      3. They Can Be Stored Longer

      Chlorine tablets are easy to store because they’re in a compact, solid form — whereas liquid chlorine comes in large, heavy jugs as you need a lot more volume to get the same sanitizing power.

      The size and weight isn’t the biggest factor here, though.

      With proper storage conditions, chlorine tablets can be used up to 2 years after purchase, while liquid chlorine only has a half-life of only 3 months. This allows you to bulk-buy tablets and keep them handy for multiple seasons.

      It’s also worth mentioning that liquid chlorine requires more careful handling when storing for longer periods, whereas chlorine tablets aren’t prone to spillages.

      Drawbacks of Using Chlorine Tablets

      These are the cons:

      1. They Contain Cyanuric Acid or Calcium

      Depending on which type of chlorine tablet you buy, it will either contain cyanuric acid or calcium.

      While some cyanuric acid is beneficial as it prevents the sun from breaking it down too quickly, too much of this acid also reduces the effectiveness of your chlorine. At a certain point, it can cripple your chlorine’s sanitizing power.

      Similarly, having calcium in your pool helps to prevent etching, but too much will lead to calcium scaling and lower the overall quality of your water.

      Seeing as excessive cyanuric acid and calcium levels can’t be fixed without partially or fully draining the pool and replacing the water, long-term use of chlorine tablets can be problematic.

      2. They Reduce the pH of the Water

      Most chlorine tablets are acidic, so they will slowly drag down the pH and total alkalinity of your pool water.

      When the pH level falls too low, it not only makes the water harsher on your skin and eyes, but it also wears on your pool surfaces and equipment. This effect is very subtle at first, but it will be more apparent as your pH level continues to decline.

      Liquid chlorine works differently.

      While the liquid itself does have a high pH of around 13, it quickly breaks down in the water and begins interacting with contaminants right away. As a result, any change in pH is lost as the chlorine gets used up, making it effectively pH-neutral.

      3. They Don’t Allow for Quick Adjustments

      Chlorine tablets are slow-dissolving, which means the chlorine is released into your water at a slow rate.

      In other words, if your sanitizer level significantly drops as a result of a spike in contamination (high pool usage, a run of bad weather, etc.), you can’t expect to make up that difference using tablets. At least not for a while.

      Liquid chlorine is ideal for such situations, which is why it’s often used alongside chlorine tablets when a quick bump in sanitizer is needed.

      Verdict: Liquid Chlorine vs Chlorine Tablets

      Wrapping up, either liquid chlorine or chlorine tablets can be used as a regular sanitizing agent for your pool.

      Liquid chlorine is fast-acting, doesn’t contribute to excess stabilizer or calcium, and allows for more precision over your chlorine level. Overall, it’s a good option for pool owners who prioritize water quality and have more time to put into it.

      Chlorine tablets are convenient, easy to use, and provide a consistent release of chlorine that allows for a more hands-off approach to pool care. Overall, these are great for busy pool owners who just need a quick, simple solution.

      All in all, while liquid chlorine lacks much in the way of convenience, it’s fair to say this type of chlorine is objectively better for your water in the long term.

      As a final note, they can also be used interchangeably or alongside one another to give you the best of both worlds, though this can be harder to manage than simply sticking with one approach.

      Categories: Pool Care, Pool Chemistry