Unstabilized Chlorine Vs Stabilized Chlorine for Pools Explained

Michael Keenan


Pool Water Chemistry

What’s not to love about a new pool or tub? Having a pool or hot tub can be great fun, but it also comes with responsibility – like cleaning and maintenance! One of the first things you’ll need to learn about is chlorine, including its two forms: stabilized chlorine and unstabilized chlorine.

Today I’m going to explain all about these two forms of chlorine and their uses in keeping pools safe and clean. Find out why each type should be used at different times, as well as how too much stabilizer can be harmful! Keep reading for all the details about using chlorine in your pool.

One of the aspects of pool ownership that many folks find especially thorny is all the different chemicals that you require to keep your pool in top shape. That’s why I created that main guide covering most of the common pool chemicals you are going to come across.

Here’s a 101 on stabilized and unstabilized chlorine to help you take your first step towards mastering pool chemicals!

unstabilized chlorine vs stabilized chlorine

Quick Answer:

Unstabilized chlorine is a type of chlorine that does not contain cyanuric acid, which makes it more vulnerable to the sun’s ultraviolet (UV) rays. It works best with indoor pools and can be used as pool shock. It won’t last as long in the pool and requires more frequent doses of chlorine.

Stabilized chlorine contains cyanuric acid stabilizer, which helps the chlorine remain effective longer in outdoor pools. However, too much cyanuric acid can reduce the effectiveness of the chlorine, so you must ensure proper levels are maintained.

Ultimately, whichever type you choose depends on your individual needs for your pool. Read on for all the details.

Unstabilized Chlorine

Stabilized chlorine is stabilized because of a certain compound called cyanuric acid. This acid not only stabilizes chlorine but also makes it remain longer in the pool water, by preventing ultraviolet rays from the sun from eating up the chlorine.

Therefore, unstabilized chlorine is as simple as chlorine without the cyanuric acid. This chlorine dissipates faster and doesn’t sanitize as strongly as stabilized chlorine, which means you’ll have to keep replenishing the amount in the water.

Sodium hypochlorite is a disinfectant often used in pool care that is an example of unstabilzed chlorine. Cacium Hypochlorite is also unstabilized – cal-hypo – often used as a strng pool shock. See those guides for all the details.

So with so much going against it, why do we need unstabilized chlorine at all? Well, unstabilized chlorine is necessary for the following reasons:

  • It’s a good “shocking” agent.
  • It’s a quick fix to adjust chlorine levels when your pool is working overtime.
  • Since UV rays are the problem, you can use unstabilized chlorine in indoor pools without any worry!

It’s necessary to bear in mind that without a stabilizing agent, the chlorine in your pool won’t stay in the water for too long. Therefore, it’s necessary to frequently check the water and ensure that the chlorine level stays at 3 parts per million (PPM). You’ll have to keep adding chlorine to maintain this figure.

chlorine pool

Stabilized Chlorine

No prizes for guessing this one – if you’ve been paying attention, you know that stabilized chlorine is simply chlorine with cyanuric acid in it! As mentioned earlier, cyanuric acid protects the chlorine, keeping it in your pool much longer and ensuring that it’s always working to the best of its ability.

If you’re using stabilized chlorine, you don’t have to worry as much about your pool’s cleanliness, frequent checks to ensure the chlorine level is right and constantly adding chlorine to the pool to maintain the ideal level, as you probably would with unstabilized chlorine.

Therefore, stabilized chlorine is sworn by for the following reasons:

  • You save a ton of money by not having to constantly buy chlorine.
  • It reduces the amount of chlorine used in the pool without any compromise on the safety of the pool.
  • It means less time, money and effort invested.

However, stabilized chlorine isn’t all as perfect as it seems to be. Extremely high levels of cyanuric acid render the efficiency of the chlorine useless, which naturally, is counter productive. This is known as chlorine lock – see my guide for more info.

To combat excess cyanuric acids in your pool, you’ll have to dilute the water till the ideal level is reached. Read about ways to reduce cyanuric acid in your pool here.

What Type of Chlorine to Use in Your Pool?

Since it’s all chlorine at the end of the day, does it really matter which type of chlorine you use in your pool? Long story short, yes, but this depends on what kind of pool you have.

Unstabilized chlorine is excellent for indoor pools and is a great shocking agent. If you have an outdoor pool and don’t want to spend a fortune in terms of money and time on maintaining your pool, stabilized chlorine is a must.

If you’re using unstabilized chlorine, you can add cyanuric acid – just make sure the level is less than or equal to 100 PPM.

clean pool water with chlorine


What are the differences between unstabilized and stabilized chlorine for pools?

Unstabilized chlorine is a form of chlorine that is not protected from UV light, meaning it breaks down quickly and needs to be replaced more frequently than stabilized chlorine. Stabilized chlorine contains a chemical stabilizer that helps protect it from the sun and lasts longer in the pool.

How do I know if my pool needs unstabilized or stabilized chlorine?

Generally speaking, outdoor pools require stabilized chlorine whereas indoor pools can use either unstabilized or stabilized chlorine.

Are there any benefits of using stabilized chlorine in a pool?

Stabilized chlorine is beneficial because its lifespan is significantly longer than unstabilized chlorine and it provides better protection against algae growth due to its increased resistance to UV light.

How often should I use unstabilized or stabilized chlorine in my pool?

How often you need to add chemicals depends on a variety of factors such as pool water temperature, number of swimmers, amount of rainfall, and size of the pool so it’s best to check with your local pool expert for advice specific to your individual set up.

What types of problems can arise from using the wrong type of chlorine in a pool?

Using the wrong type of chlorine in a pool can lead to an imbalance in pH levels which can cause cloudy water, eye irritation, or even skin rashes if left unchecked for too long.

The Bottom Line

All said and done, though, whether you’re using stabilized or unstabilized chlorine, it’s important that you use chlorine!

Your pool needs to be safe, sanitized and clean at all points and both stabilized and unstabilized chlorine will help you with these needs. Therefore, it all comes down to what you’re more comfortable with and what your pool actually needs.

Unstabilized chlorine is great for indoor pools as well as shocking when needed, while stabilized chlorine is better suited for outdoor pools as it lasts longer without needing constant replenishment. Just make sure to check the levels to ensure everything stays within safety limits!

Now that you know the what, why, pros and cons of stabilized and unstabilized chlorine, educate yourself on the other chemicals that your pool needs, to have a safe, healthy and clean swimming pool.

michael keenan author

Author - Michael Keenan

I'm Michael Keenan the owner and creator of the Outdoor Care Guide. I'm a trained horticulturist with over 30 years of experience in pool care, plant care, and landscape care! Seemed like a good idea to share - I think I can make your life easier and save you some time and money!