What’s the Difference Between Stabilized and Unstabilized Chlorine?

Written by Michael Dean
February 22, 2024

stabilized vs. unstabilized chlorine

The most important chemical in a pool is chlorine. Being the primary disinfectant in your pool water, having the proper chlorine levels will keep your pool clean and safe. There are several different types of chlorine that you can use in your pool, and one of the main decisions you’ll need to make is choosing between stabilized and unstabilized chlorine.

Let’s dive into the differences between stabilized and unstabilized chlorine and discuss which one you should use.

Main Takeaways

  • Stabilized chlorine contains an additive, like cyanuric acid, that stops the chlorine from breaking down under the sun’s UV rays. Dichlor and trichlor are stabilized chlorine.
  • Unstabilized chlorine contains no such additives and is the better option for indoor pools.
  • Stabilized chlorine is best for outdoor pools, but make sure to keep an eye on the cyanuric acid levels.
  • Alternatively, you can use unstabilized chlorine and add CYA separately.

What Is Stabilized Chlorine?

Stabilized chlorine is a pool product that does not break down due to its chemical bonds when exposed to sunlight. Usually, an additive, like cyanuric acid, is added to the chlorine to make a stabilized chlorine compound. Using stabilized chlorine will allow you to change the chlorine content less regularly.

In The Swim 3 Inch Stabilized Chlorine Tablets

These basic trichlor tablets are perfect for most swimming pool owners.

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Stabilized chlorine is helpful for outdoor pools that get direct exposure to sunlight. Due to the sun’s ultraviolet rays, unstabilized chlorine will break down after a long enough exposure. Sunlight exposure will lead to a less chlorinated pool, which means a less disinfected pool. Stabilized chlorine fixes that problem. The cyanuric acid added to the chlorine creates a compound not affected by the sun’s rays, thus not allowing the chlorine to escape the swimming pool.

Compounds such as dichlor and trichlor are examples of stabilized chlorine compounds. Trichlor has a much higher level of chlorine than dichlor, but your choice of which exact product to use will ultimately rely on the specifics of your pool.

For example, if your pool has an algae problem, then trichlor won’t be your best bet, as this type of chlorine is slow-dissolving and won’t raise the chlorine levels fast enough to take care of this problem. On the other hand, dichlor is a fast-dissolving chlorine, making it a great choice for a pool shock.

What Is Unstabilized Chlorine?

Unstabilized chlorine is just chemical chlorine with no additives. In other words, the common additive in stabilized chlorine, cyanuric acid, is not present in unstabilized chlorine. This means that if the pool gets exposed to direct sunlight, the chlorine inside will react to the sunlight and break down.

Unstabilized chlorine is effective for use in indoor pools. Due to the lack of direct sunlight, the problem of chemical breakdown is averted. However, this doesn’t mean you can’t use unstabilized chlorine for outdoor pools. In fact, liquid chlorine and cal hypo (two types of unstabilized chlorine) are incredibly popular amongst outdoor pool owners. To use it, always add cyanuric acid separately and ensure the levels are between 30 and 50 ppm; otherwise, the chlorine will break down very quickly, rendering the chlorine’s disinfectant properties useless.

Unstabilized chlorine products require more maintenance to make sure chemical levels stay regular. This maintenance requires daily measurements of chemicals. You’ll want to monitor the chlorine (and CYA) levels on days when you use your pool heavily.

In The Swim Calcium Hypochlorite Chlorine Granular Pool Shock

In The Swim has a reliable cal hypo shock that is effective and easy to use.

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Key Differences Between Stabilized and Unstabilized Chlorine

Depending on the sort of pool you have, including whether it’s an indoor pool or not, the type of chlorine you choose should lead to a more efficient disinfecting routine.

Cyanuric Acid Content

As mentioned, stabilized chlorine has the additive cyanuric acid, whereas unstabilized chlorine does not. Cyanuric acid bonds with the chlorine compound, changing the chemical composition. CYA acts as a sunscreen for the chlorine, protecting it from breaking down in the sun.

Chlorine Top-Ups

Managing a pool’s chemical content is more straightforward with stabilized chlorine because it loses less chlorine on a daily basis. Less chlorine loss means you won’t have to continually add or balance your pool’s chemical content. Unstabilized chlorine is recommended for indoor pools, but you will still need to check chemical content regularly.


On a related note, since you’ll be using less chlorine over a period of time when using stabilized chlorine, you can also save a bit of cash compared to using unstabilized chlorine in an outdoor pool. Plus, with unstabilized chlorine, you also need to purchase cyanuric acid separately.

Cyanuric Acid Levels in Your Pool

While stabilized chlorine is a great option for outdoor pools, issues can arise when there’s simply too much stabilizer in the water. Too much cyanuric acid in your pool makes the acid bind with all of the chlorine, creating an environment ripe for bacteria growth. Free chlorine holds disinfectant properties, so if it’s not present due to an abundance of cyanuric acid, the pool will not be able to stay clean.

Having cyanuric acid levels that are too high is one of the biggest problems a pool owner can face. Cyanuric acid never breaks down, meaning it accumulates in the pool. This accumulation will lead to less and less effective chlorine over time. The only way to fix this issue is to partially or fully drain the pool, adding new, fresh water and unstabilized chlorine until you have the right chemical balance.

This is one of the major disadvantages of stabilized chlorine. It’s much harder to control exactly how much CYA is present in your pool. On the flip side, with unstabilized chlorine, you can test your CYA levels and add the exact amount of chemicals you need to raise the levels to 30 to 50 ppm as needed.

Stabilized Chlorine vs Unstabilized Chlorine: Which Is Best for You?

Stabilized chlorine is the best choice for outdoor pool owners. Due to stabilized chlorine’s ability to withstand the sun’s ultraviolet rays, it can last longer with less oversight in an outdoor environment. If you have the right mixture of chlorine and cyanuric acid, your pool will stay clean with little effort on your part. Just test the pool water and add as needed.

Unstabilized chlorine is recommended for indoor pools because it is better at disinfecting your pool, but only when not exposed to direct sunlight. Without the cyanuric acid content, the ultraviolet rays will break down the chlorine, leaving your pool needing more chlorine. But with all that said, you CAN still use unstabilized chlorine for your outdoor pool, as long as you maintain the cyanuric acid levels separately.

Another nuance worth considering is that if you already have too much CYA in your pool, it might be better to use unstabilized chlorine, as too much CYA comes with problems of its own.

And that’s about it! If you’re looking for other pool care tips, make sure to read my guide on swimming pool maintenance.

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Frequently Asked Questions

Is Pool Shock Unstabilized Chlorine?

Not necessarily! Unstabilized chlorine simply means the chlorine type does not have any cyanuric acid. Liquid chlorine and cal hypo are used as chlorine shock, but dichlor, a stabilized chlorine, can shock the well.

Can You Mix Stabilized and Unstabilized Chlorine?

You cannot mix them or even store them next to one another! This can lead to a dangerous chemical reaction. However, you can use cal hypo to shock your pool when using trichlor for your standard chlorine treatment. But make sure the dry chemicals do not come into contact with one another!

Can You Add Too Much Chlorine Stabilizer?

Definitely! You should maintain your stabilizer, or cyanuric acid, levels at around 30 to 50 ppm. Any higher and it can interfere with the effectiveness of the chlorine! If you have too much stabilizer, here’s my guide on how to lower CYA levels.

Go Chlorinate Your Pool

Whether you choose stabilized or unstabilized chlorine is entirely up to you! Both types of chlorine are super effective. And if you have an outdoor pool and are using unstabilized chlorine, just make sure to top up with enough CYA to protect the chlorine from the sun’s UV rays.

Have more chlorine questions? I’m here to help! Just shoot me a note.

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