Home » How Long Does Pool Chlorine Last For (Shelf Life)?

How Long Does Pool Chlorine Last For (Shelf Life)?

So you’re thinking about buying chlorine for your pool in bulk, but you’re unsure how long you can store it. In this article, we’ll be showing you the shelf life of chlorine, in various forms, as well as tips on how to make chlorine keep longer.

Liquid chlorine has an effective shelf life of 6 months. Chlorine tablets and granules have a shelf life of 12 months to 5 years. Temperature extremes (hot or cold) and high humidity can all affect how long chlorine will last and the extent of chlorine degradation.

Before going into the details, let’s first see how chlorine breaks down and if it differs between the various forms.

Pool chlorine and other cleaning equipment beside the pool
Pool chlorine and pool cleaning equipment beside the pool.

Does Pool Chlorine Go Bad or Expire?

Pool chlorine, like almost every other pool chemical, does go bad, usually within a few years. How it happens and at what rate depends on the specific type.

We’ll cover the different types of chlorine further below.

Liquid Chlorine (Bleach or Sodium Hypochlorite)

liquid chlorine piles in store
Pool liquid chlorine.

Does Liquid Chlorine Go Bad?

Liquid chlorine, otherwise known as sodium hypochlorite, is an unstable form of chlorine that will lose 38% to 74% of all of its potency within 6 months. Specific environmental conditions can cause it to degrade even faster.

How Long Does Liquid Pool Chlorine/Bleach Last (Keep)?

Liquid chlorine will not lose 25% of its potency in 2 weeks to 3 months depending on how it was stored. When buying liquid chlorine for the pool, plan to use it within 1 month, less if you’re storing it in temperatures

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Out of all the forms of chlorine, liquid chlorine lasts the shortest amount of time. Even if it’s kept in an airtight container under cool and dry conditions it will degrade and lose its potency over time.

If left exposed to hot temperatures, cold temperatures, and/or direct sunlight, this will shorten the life of liquid chlorine from a few months to a week or two.

When purchasing pool chlorine, it’s best to use it within 2-4 weeks of the manufacture date to ensure its freshness. The date should be printed on the side of the package.

Does it Lose Potency?

Liquid chlorine (aka sodium hypochlorite/bleach) will begin to lose its potency immediately after it’s manufactured. Within 6 months, it can lose up to 38% of its potency and up to 74%. And if stored in hot, cold temperatures or direct sunlight, it’ll become ineffective at an even faster rate.

This chart shows the degradation time and storage temperature for 12.5% liquid chlorine (bleach or sodium hypochlorite) to lose 25% of its strength:

Liquid Chlorine/Bleach Shelf Life Vs Storage Temperature in Weeks

This table shows the storage life in weeks and months of chlorine/bleach:

Storage TemperatureShelf Life
100ºF1-2 weeks
90ºF2-3 weeks
80ºF4-6 weeks
70ºF3 months
*data sourced from Odyssey Manufacturing

This chart shows the degradation time and storage temperature for liquid chlorine (bleach or sodium hypochlorite) to lose 50% of its strength:

Liquid Chlorine/Bleach Shelf Life Vs Storage Temperature in Months
Storage TemperatureShelf Life
100ºF1 month
90ºF2-3 months
80ºF4-5 months
70ºF7-9 months
*data sourced from Odyssey Manufacturing

Chlorine Tablets (Pucks)

Pool chlorine tablets
Pool chlorine tablets.

There are 3 main types of tablets (pucks) used for swimming pools, spas, and hot tubs. They are:

  • Dichlor
  • Trichlor
  • Calcium Hypochlorite (cal-hypo)

Do Chlorine Tablets Go Bad

Chlorine tablets do go bad but it takes many years. Depending on which type you use (dichlor, trichlor, or cal-hypo), you’ll have differing shelf lives.

How Long Do Chlorine Tablets (Pucks) Last (Keep)?

The shelf life of chlorine tablets is usually at least 3-5 years or even more provided they are stored correctly. This goes for dichlor, trichlor, and cal-hypo pucks.

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The main thing that will shorten the shelf life of chlorine tablets is moisture. Heat is a secondary factor. 

When we talk about moisture, there are two types:

  • Humidity
  • Splashing

Humidity Moisture from the air will eventually penetrate chlorine tablets and degrade them.

Splashing – spilling water or splashing water on chlorine tablets will quickly degrade them and shorten their life.

The best thing you can do to extend the shelf life of your chlorine tablets is to keep them out of warm temperatures and make sure they are stored in a sealed container. Temperatures of 50-70°F (10-21°C) are ideal.

You want to also keep water splash away from the tablets. And preferably store them in an area with low humidity.  

Do Chlorine Tablets Lose Potency?

After three years of being placed under optimal environmental conditions, In The Swim found their trichlor chlorine tablets were found to still have 98% of their originally available chlorine. Being wrapped individually in plastic, they were found to still be viable after 5 years.

Related Reading: How Many Chlorine Tablets Do You Need in Pool or Floater?

Chlorine Granules

Granular chlorine with scoop in a plastic bag.
Granular swimming pool chlorine.

Dichlor and cal-hypo or the main types of chlorine that come in granular (powder) form. These chlorines are commonly used in pools and hot tubs for chlorination. Cal-hypo is also sold as Pool Shock.

Do Chlorine Granules Go Bad?

Granular chlorine goes bad at a rate similar to chlorine tablets. If kept under proper conditions, chlorine granules can last over 5 years.  If stored incorrectly, chlorine granules will turn into a thick paste and be unusable.  This is a sign that moisture has gotten to it.

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Granular chlorine includes:

  • Calcium hypochlorite (aka cal-hypo)
  • Dichlor

How Long Do Chlorine Granules Last (keep)?

Both calcium hypochlorite and dichlor have their own shelf life, but generally, chlorine granules can last over 5 years if stored properly.

To extend the life of chlorine granules, store them in cool dry conditions. You may also repack the granules into freezer bags to keep the moisture out. Rather than leave them in the bucket they came in.

Related Reading: Liquid Chlorine Vs Tablets – What’s Better for Your Pool?

Does Pool Shock Go Bad?

Pool shock can go bad in as little as 12-24 months if it is not stored correctly. If moisture gets to it, it will turn into a paste-like mush and be unusable.  Pool shock usually comes in granular form and it is the chlorine type, calcium hypochlorite (cal-hypo).

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Like the other dry chlorine types, even if water isn’t splashed directly on the pool shock, the moisture in the air can ruin it.

To maximize the shelf life of the pool shock, store it in a cool area between 50-70°F (10-21°C).  Keep it in a sealed bag with low humidity too. You can store it in freezer bags to extend its life.

Related Reading: Which Pool Shock Should You Use? (answered!)

Does Chlorine Keep Longer Unopened?

Liquid chlorine or bleach will not last or keep longer unopened. Liquid chlorine is unstable and will naturally degrade. Chlorine tablets and granules, however, will last longer if unopened and packed well. Both can last roughly 3+ years if stored in airtight containers in a cool and dry area.

Tips to Increase Chlorine Shelf Life

Now that we’ve gone over the shelf lives of the different versions of pool chlorine, let’s take a look and see what actions you can take to prolong your chlorine products to ensure you’ve used every bit of what they can offer.

  • Make sure to store your chlorine products separately away from other chemicals and chlorines. This will ensure their effectiveness and reduce your chances of having a dangerous reaction take place
  • Keep at a temperature between 40°F (4.4°C) and 85°F (29.4°C) to prevent degradation due to the heat or cold
  • Store in a well-ventilated area so that the products don’t have a chance to react with water in any way (including humidity)
  • Keep your chlorine products in a dark area away from the sun, preferably in individual containers. This prevents UV light from speeding up the degradation process

Tips on Purchasing Chlorine Products

Before purchasing your chlorine products, be sure to take a look at some of the tips listed here so that you can prevent any unnecessary work in storing them later on.

  • You should only buy what is necessary since any additional product you don’t use will degrade eventually. This is especially true for liquid chlorine, which will degrade in a matter of months
  • Try to check the manufacture date before purchase to ensure you have the freshest chlorine
  • Estimate how much pool chlorine you’ll be using (based on pool size, type of product, etc.) so that you can purchase exactly what is needed and ensure none will go to waste

Final Thoughts

Now that you’re aware of how long different pool chlorine products last, hopefully, you’ll now be able to make informed decisions on which product and how much of it you’ll need to buy. As long as you’re aware of its shelf life, you can decide on how much you’ll need for your situation so that you ensure you’ll never have to waste your time or money on an unused product.

Related Reading: Can You Use Clorox or Bleach in a Hot Tub?

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