Trichlor: Should You Use This Type of Chlorine in Your Pool?



Ahh, chlorine. Such a crucial part of pool care and yet there’s so much conflicting information about which type you should use.

Whether you own a pool or just maintain one, getting to grips with chlorine, how it works, and what differentiates the various types available can sometimes feel like going back to chemistry class.

So today, we’ll be demystifying one type of chlorine in particular; trichlor.

What Is Trichlor?

Trichlor—or “Trichloro-S-Triazinetrione” if you’re feeling adventurous—is a type of chlorine that’s commonly used in swimming pools. (Thanks, Captain Obvious!)

You’ll typically find this in the form of 1″ or 3″ tablet that looks almost like a hockey puck (which is where the term chlorine pucks come from). The tablets are slowly dissolved and drip-fed using an automatic chlorinator, a floating dispenser or sometimes the pool skimmer.

Rx Clear 3' Inch Stabilized Chlorine Tablets | 50 Pounds | Individually...
Rx Clear 3" Inch Stabilized Chlorine Tablets | 50 Pounds | Individually...

    The tablets come in at a pH level of around 3 so it will slightly lower your pools pH and total alkalinity after use. Trichlor is also the strongest tablet on the market, containing around 90% active chlorine along pool stabilizer (cyanuric acid) for protection against the sun.

    Trichlor can also be found in power/granular form, but this is typically used as a shock treatment and is much less common — especially since other, arguably better shock treatment products are available.

    Trichlor Quick Stats

    • Comes in tablet (most common) or granular form
    • Both forms have a pH of around 3
    • Contains around 90% active chlorine
    • Contains pool stabilizer (cyanuric acid)

    How Does Trichlor Chlorine Work?

    Trichlor sanitizes your pool water the same way other chlorine types do.

    Once dissolved and released into the water, it turns into hydrochloric acid that combines with microorganisms and other nasties, breaking down their cell walls and disrupting their chemical structures (almost like a clingy girlfriend).

    This “combined chlorine” is also referred to as chloramines, and chloramines are pretty harmless until they build up too much in the water — but that’s where regularly shocking your pool comes in.

    While trichlor works in much the same way as other types of chlorine, like calcium hypochlorite or liquid chlorine, there other factors to consider when choosing the best chlorine product for your specific pool.

    Let’s talk about that next.

    The Pros and Cons of Trichlor

    Considering trichlor tablets to chlorinate your pool?

    So far I’ve just thrown a bunch of descriptions and facts at you, but I’ve yet to talk about what these mean from a practical standpoint, and more importantly, if trichlor is even a smart option for sanitizing a pool.

    Rx Clear 3' Inch Stabilized Chlorine Tablets | 50 Pounds | Individually...
    Rx Clear 3" Inch Stabilized Chlorine Tablets | 50 Pounds | Individually...

      The Benefits of Trichlor

      • It’s very strong, so you’ll need to use less product to reach the required level of free chlorine in your pool, which is around 3 parts per million (ppm).
      • It’s “set and forget” since they’re slow-dissolving tablets, meaning you don’t have to manually add chlorine to your pool everyday unlike when using liquid chlorine.
      • It’s fairly easy to transport as it comes in varying sizes of containers. Buying them locally isn’t too difficult, and shipping costs are reasonable too.
      • It has a long shelf life, so you can stock up and get your chlorine tablets from the same batch season after season, without having to worry about potency issues.
        It’s very affordable. In fact, it’s one of the cheapest types of chlorine you can buy after sodium hypochlorite (liquid chlorine), alongside calcium hypochlorite.

      The Drawbacks of Trichlor

      • It’s highly volatile and potentially explosive when mixed with calcium hypochlorite (often used for shocking a pool). Be careful not to mix trichlor with the wrong chemicals because even the residue of can trigger a reaction.
      • It can stain or even rust your pool surfaces if used incorrectly, as any accidental buildup (or “pooling”) of dissolved trichlor is highly acidic. An automatic chlorinator is the best way to prevent this, and often the best way to add chlorine to your pool overall.
      Pentair R171096 Rainbow 320 Automatic In-Line Chlorine/Bromine Feeder For...
      Pentair R171096 Rainbow 320 Automatic In-Line Chlorine/Bromine Feeder For...

        Other Potential Benefits/Drawbacks

        The following points can either be benefits of drawbacks depending on the current state of your pool water chemistry:

        • It’s stabilized, meaning it contains cyanuric acid which gives it protection from the sun. This is great as it’s necessary for daily chlorination, however regular use raise your cyanuric acid level much. This will eventually weaken your chlorine.
        • It has a low pH, so it will lower your pools pH and alkalinity levels over time. This can be useful if you coincidently need to lower your pH, but inconvenient if you don’t. You can use baking soda or soda ash to bring the pH level back up, however.

        Why It’s Ideal for Daily Chlorination

        Keeping your pool properly chlorinated is an ongoing task, and the type of chlorine you decide to use will either make that job easier, or harder. Trichlor tablets are a great choice for a few reasons.

        First of all, the fact that you can just pop these tablets in a floating dispenser or automatic chlorinator and let them work is a HUGE convenience — unlike calcium hypochlorite or liquid chlorine, which usually have to be added manually.

        Also, you don’t have to worry about calcium hardness issues since it doesn’t contain any calcium (like calcium hypochlorite), and they’re among the cheapest types of chlorine on the market.

        It sounds like a no-brainer, but there is a catch.

        Since trichlor tablets are about half cyanuric acid (pool stabilizer), they will continue to raise your cyanuric acid level over time. The higher this gets, the weaker your chlorine gets, and the more you need to add to properly sanitize your pool water.

        Cyanuric acid doesn’t degrade, so you’ll need to keep an eye on the level throughout pool season to make sure it doesn’t get too high. Eventually, you will likely need to swap to a non-stabilized chlorine product, like cal-hypo or liquid chlorine.

        Note: Until recently, the only way to lower cyanuric acid was to dilute it, either by praying for rain or partially draining the water and refilling. Nowadays, thanks to science, you can actually buy cyanuric acid reducer.

        Why It’s Bad for Pool Shocking

        When combined chlorine (chloramine) builds up too much in your pool, not only will it give off that familiar chlorine smell, but it also prevents free active chlorine from effectively doing its job, as well as causing skin and eye irritation.

        Removing chloramines involves shocking your pool once a week, which is when you add 10x the amount of free chlorine as there chloramines. This destroys the combined molecules, forcing them to leave the water through oxidation. (Shocking is also used to fight a sudden algae bloom, or certain “accidents” in the water).

        You can shock your pool with any type of chlorine as long as you add enough of it, but in most cases, you’re not just adding chlorine; you’re adding a large volume of other chemicals mixed in with it.

        Using trichlor granules for shocking is a classic example. It’s stabilized, so not only will it take longer to burn off the huge chlorine spike due to it being protected from the sun, but you’re adding even more cyanuric acid to your pool. (Hint: don’t do it)

        So what should you use for shocking?

        Calcium hypochlorite is another granular form of chlorine but it’s unstabilized (no cyanuric acid), and it’s widely used for shocking. Sodium hypochlorite (liquid chlorine) is another alternative, and it even comes pre-dissolved.

        In The Swim Pool Shock – 68% Cal-Hypo Granular Sanitizer for Crystal...
        In The Swim Pool Shock – 68% Cal-Hypo Granular Sanitizer for Crystal...


          Trichlor tablets are very common across the industry. They’re ideal for daily chlorination thanks to the “set and forget” nature of tablets in general, but they do add cyanuric acid to your pool which can potentially push your pool chemistry out of balance.

          As long as you’re keeping a regular eye on your levels, however, you’ll be able to switch to a stabilized chlorine (like liquid chlorine) to prevent this from happening. If you prefer a single approach, then trichlor may not be the best option.

          Good luck and happy swimming!

          Categories: Pool Care, Pool Chemistry