Stabilized vs. Unstabilized Chlorine: Which One Should You Use?

Stabilized vs. Unstabilized Chlorine

There are several chemicals you will need to maintain your swimming pool. Experienced pool owners already know most of them, but new ones tend to have difficulties, especially when deciding between two that sound pretty similar such as stabilized and unstabilized chlorine.

While stabilized and unstabilized chlorine have several similarities, they differ in their best uses, and so it is essential to understand what each is all about and when to add it to your pool.

What is Stabilized Chlorine? 

Stabilized chlorine is the type that includes cyanuric acid as part of its formulation. Cyanuric acid aims to make it a more stable compound so that it does not break down and deteriorate fast when exposed to the sun’s UV rays.

Stabilized chlorine is available in two types, which are sodium dichlor and trichlor. However, trichlor is often the most preferred option as it is more effective at sanitizing since it has up to 90% active chlorine.

With stabilized chlorine, you can prolong the service life of chlorine in your pool by up to 5 times. Hence, you will not need to keep adding more frequently, which saves you money and a lot of time. Also, this chlorine type will be great for use in outdoor pools.

However, stabilized chlorine can also have some shortcomings, given that when the cyanuric acid levels get too high, they render it ineffective at cleaning the pool water.

Read more: How to Lower High Cyanuric Acid in Pools

What is Unstabilized Chlorine? 

Unstabilized chlorine does not include any pool stabilizer (cyanuric acid) in its formula. Hence, the chorine is not very stable. Exposure to the sun’s UV rays can reduce the amount of unstabilized chlorine in pool water by up to 90% in just a few hours.

You can get unstabilized chlorine in 3 main forms: sodium hypochlorite, calcium hypochlorite, and lithium hypochlorite. Calcium hypochlorite is the most common type as it has up to 78% of available chlorine.

With this chlorine type, you will not get as much sanitizing power as when using stabilized chlorine. Also, since it breaks down quickly, you have to keep adding more chlorine almost every day, which is expensive, laborious and time-consuming.

That said, the instability of this chlorine type makes it the best choice for shocking pools as you can add large amounts with no worries since it will dissipate super fast. Unstabilized chlorine is also best for indoor pools where you do not need to worry about the sun’s rays breaking it down.

Similarities Between Stabilized and Unstabilized Chlorine

The main similarity between stabilized and unstabilized chlorine is that both are effective at sanitizing the pool.

Also, both use hypochlorous acid to attack the cell walls of the contaminants and oxidation to render them inert.

Another similarity is that you can get both in different forms including, liquid, powder, tablet and granular form.

Differences Between Stabilized and Unstabilized Chlorine

The most significant difference between the two chlorine types is that stabilized chlorine will include cyanuric acid (pool stabilizer), while unstabilized chlorine will not.

Additionally, the amount of available chlorine is often quite different. With stabilized chlorine, you can get up to 90% available chlorine from trichlor chlorine.

However, most unstabilized chlorine types have much lower available chlorine. Calcium hypochlorite will give you the highest amount, but it never goes beyond 78%.

The typical applications are also different. Stabilized chlorine is often preferred for continuous sanitization. On the other hand, unstabilized chlorine works best as a pool shock.


Stabilized and unstabilized chlorine are valuable chemicals for maintaining swimming pools, and it is always best to have both around. However, what you use largely depends on your specific situation.

If you have an outdoor pool and want a reliable chemical for day to day sanitization, stabilized chlorine is a perfect choice. However, you still need unstabilized chlorine for the occasional pool shocking.

Indoor pool owners are at liberty to use either stabilized or unstabilized chlorine. Since the sun is not a significant factor indoors, even unstabilized chlorine tablets can still be effective enough.

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