Can pool chlorine tablets go bad?

Welcome back students of swimming pool ownership. In this lecture, we look at chlorine shelf life and the reasons that cause them to expire. In the ideal world, the pool care ends when you use up the last chlorine tablet, perform some “pool shock,” and adjust the balance of your water.

Before you can make the most chlorine, it’s good to determine the shelf life of these products – it will help save you from a lot of hassle!

How to Maintain the Effectiveness of Water Purification Tablets

It’s vital that you maintain chlorine tablets under the right temperatures, which are usually between 15 to 30 °C (60 and 86 °F). To be specific, these are conditions that ensure the product stays productive up to the chosen expiration date. Also, ensure you keep your tablets in a dry and cool place.

It’s best to keep them away from issues such as moisture or heat, to maintain the effectiveness of the tablets. Also, ensure you seal the cap tightly, and ensure you don’t use the tablets for more than one year. On the contrary, iodine has an average shelf life of 6 years, with 130mg tablets expiring after seven years of use.

Do I Need to Use Chlorine Tablets in My Swimming Pool? 

Use a pool kit to test the chlorine level of your pool. You have to maintain the chlorine levels between 1 to 1.5ppm (parts per million.) That said, if the levels are lower, you may have to add chlorine levels until you get the correct level.

Choose the chlorine tablet you want to use for the pool. A 30,000-liter pool might require a 1 3” tablet (200g) each week. Also, chlorine tablets average between 1 and 3 inches. Thus, you have to use 1” tablets and three tablets that equal on the 3” tablet. Usually, 1” tablets dissolve faster than the 3” tablets, which makes them highly cost-effective.

Put the chlorine tablets into the feeder, which will let you control the rate at which the tablets dissolve. You can adjust the flow by using a control knob. Plus, you also have to understand how to open the flow control knob to maintain 1 to 1.5ppm level in the pool. In most cases, this will depend on the amount of flow available, the running the pumps, and the type of feeder available. All pools vary, so it may take some time for you to get the adjustments for your pool correct.

What Causes the Tablets to Expire?

Various factors come into play in the expiration of chlorine tablets. For instance, factors such as sunlight, temperature, and moisture will increase the degradation process of water purification tablets. As such, brand companies use brown glass bottles or foils to store tablets. Users are advised to ensure they store the tablets in the right conditions.

Exposing the tablets to factors such as extreme heat, moisture, or air will easily compromise their effectiveness. Thus, remember to replace opened bottles or pockets as soon as you can, which is usually in less than 12 months.

Furthermore, you should note that purification tablets can easily expire when left in poor conditions. It’s good to ensure you adhere to the storage recommendations on the label, to improve the shelf life of the tablets.

How to Check the Expiration of Water Tablets

Before using chlorine tablets, consider checking their color. The tablets that have green or yellowish color require immediate replacement. More so, the types that are grayish or brown are suitable for use. That said, some tablets might take five years to expire from the date of production. For this reason, replace the pills before expiration. Check the backside of each tablet foil wrap, to determine whether they are safe for use.

Once you open the chlorine tablet pack, ensure you store it the right way, which is away from humidity, sunlight, or moisture. These are the perfect conditions to ensure your product is safe for the next application.

The expiry date of a product relates to the chemical makeup of the tablet. Water purification tablets include a unique mixture of active(sterilizers) and non-active ingredients. In the ingredients list, the non-active ingredients are otherwise referred to as “Other Ingredients.” Usually, they make up for a significant amount of each tablet. More so, they not only provide tablet bulk, but they also help improve stability, solubility, and preservation of the tablets.

The main ingredients in purifying tablets, also make up for a small percentage of the tablet. This is when compared to the non-active ingredients, but all are responsible for sterilization procedures. Also, the active ingredients are usually iodine or chlorine-based. That said, you may also come across silver or mineral based forms on the market.

Expiry of Chlorine Water Purification Tablets

On average, expect chlorine tablets to expire somewhere between 3 and 5 years. The main variation, in this case, is the type of container it’s available with, and the kind of seal used. Furthermore, chlorine purifying tablets that are individually sealed will last for between 4 and 5 years. That said, tablets that are available in a plastic tub will last for 3 years on average. As such, if you want to buy chlorine water purifying tablets and want longevity, then you should be fine with the individually sealed types.

Shelf Life of Other Pool Chemicals

It would also be good to consider the shelf life of other pool products to give you a better perspective when using pool products:

Liquid Chlorine

Otherwise referred to as Sodium Hypochlorite, or chlorine bleach, liquid chlorine is a relatively unstable form of chlorine. It may lose well over 50% potency in the first few months and more than ¾ in 12 months. If exposed to hot or cold temperatures and direct sunlight, degradation might occur faster. For a stable product, consider using instant liquid chlorine in a bottle.

Tablet Chlorine

Tricolor tablets have an exceptional shelf life. According to lab tests, high-quality chlorine tablets should have lifespans of more than 36months. That said, the pills should be stored at normal temperatures, and by using a tightly closed bucket lid. In the right conditions, trichlor tablets should remain usable for over 5 years.

Granular Chlorine

Commonly referred to as “pool shock” or calcium hypochlorite, granular chlorine has a long shelf life. Ensure that you store it in a cool and dry location. You can shock a pool in 1 lb bags, and absorb moisture from humid air. Plus, the bags can dissolve within 12-24 months. For improved longevity, consider packing the chemicals in zip lock freezer bags or buckets – which are highly convenient.

Chlorine Stabilizer

Chlorine stabilizer is also commonly referred to as cyanuric acid, and its potency will stay a longer duration than most pool chemicals. Even if it absorbs moisture, it’s good to store it in a tightly sealed container. Also, ensure you label it as Stabilizer, or Conditioner, such that you won’t confuse the white powder with other chemicals. If the container label becomes unreadable, you may also need the labeling.


When stored correctly (in a cool and dry indoor location), pool algaecides are stable and high potency with a lifespan of up to 4 years. Complications such as temperatures over 75 degrees and the direct sun might compromise the shelf life of algaecides. This occurs mainly in lower concentration algaecides, but freezing temperatures can also compromise pool algaecide.


Similar to algaecides, pool clarifies have a long shelf life that might average at 4 years and more. It’s best to store them in tightly closed and cold temperatures for the best results. Plus, outdoor storage in a garage or shed in high temperatures can compromise the effectiveness of the clarifiers.  More so, freezing can compromise the polyamide structure, thereby affecting the


Keeping your swimming pool cool is a crucial factor to consider, especially if you have several users. As a savvy pool owner, you can start by how to tell if your chlorine tablets have gone bad. When you can keep track of the quality of these tablets, you will enjoy a clean pool and longevity. Furthermore, bad tablets are likely to cause a health concern and even waste your investments as well. For this reason, keep track of chlorine tablet use, and ensure you use them at the right point in time.