Chlorine tablets for pools: What You Must Know


What is chlorine?

Chlorine is a chemical element that can be found in rocks and ocean water. It is also a chemical that allows us to drink water safely without worrying about contamination.

Furthermore, chlorine plays an important role in producing silicon-based semiconductors and PVC building materials.

Just like drinking water, we need chlorine to keep our pool water clean.

How does chlorine work?

When chlorine reacts with water, it forms a few different compounds, such as hypochlorous acid, hydrochloric acid, and hypochlorite ions.

The pH of your pool water determines how much of these compounds are present. If your pool has a higher pH, you will see more hypochlorite ions in the water.

These compounds alone don’t do much for keeping your pool contaminant-free.

If the pH of your pool dips below, there will be more hypochlorous acid, which acts as a disinfectant for bacteria and viruses in your water.

There are six common types of chlorine that are used for water chlorination:

  1. Gas chlorine – Expensive and dangerous with a low pH, so it’s rarely used in modern days
  2. Cal-hypo – The oldest form of chlorine. It has a high pH and often comes in granular or tab forms. It’s volatile and highly reactive with other compounds. Too much of it can cloud your pool water
  3. Sodium hypochlorite – It is also commonly known as bleach. It’s a fast-acting compound with a high pH. It works well for shocking and increasing chlorine levels rapidly.
  4. Trichlor – It usually comes in 1-inch or 3-inch tablet form. It can also be found in granular form. This form of chlorine contains quite a bit of cyanuric acid and has a low pH. Trichlor is especially useful in a hot environment because it endures hot weather relatively well compared to other chlorine types.
  5. Dichlor – It is found in granular form and has more of a neutral pH. It raises the cyanuric level in your pool substantially more than trichlor.
  6. Lithium – lithium is another granular form of chlorine. It does not affect pH and tends to be very expensive. It is safe for all types of pool surfaces.  

How to safely use chlorine in your pool

  • When storing chlorine, make sure you keep the lids tightly closed.
  • Store them in a dry place away from other chemicals.
  • Be careful when you open up your chlorine bucket since fumes can build up inside. Open your chlorine bucket where there’s some form of ventilation.
  • When pouring powder form of chlorine into the water, keep them close to the water as you pour, so the wind doesn’t carry them away and end up on things that we don’t want them to be on.
  • If your pool has a sensitive surface, such as a vinyl liner, you can pre-dilute your chlorine before pouring to prevent possible damage.
  • Don’t combine chlorine with other forms of gas, as it can be hazardous.

Benefits of chlorine tablets for your pool

These are some of the reasons why you may consider using chlorine tablets for your pool over other forms of chlorine.


Unlike liquid chlorine, chlorine tablets are stabilized forms of chlorine, which means it’s protected by cyanuric acid (CYA). So each time you add chlorine tablets into your pool, you are also increasing the level of cyanuric acid.

The CYA acts as a sunscreen for your chlorine, protecting against the sunlight. This is important since chlorine is extremely vulnerable to sunlight. In fact, most chlorines can become degraded in just a few hours under strong sunlight.

Ease of use

With chlorine tablets, you will normally add them into your feeder or automatic chlorinator, and they will chlorinate your pool on their own. 

All you need to do is fill up the equipment with your tablets. There’s no need to manually pour them into your pool water while you walk around the pool.

Adjust the chlorine output

If you use an automatic chlorinator for dispersing chlorine tablets, you can adjust chlorine tablets’ output using the dial. This is useful since you can turn it up or down depending on the chlorine level in your pool.

Downsides of chlorine tablets

Too much cyanuric acid

While stabilizers are essential for the proper functioning of chlorine, over-stabilizations cause chlorine to become ineffective. This is because your chlorine will slow down substantially with too much CYA present in your pool.

The result is often a cloudy pool with a high combined chlorine level.

Chlorine feeder safety hazard

Chlorine feeders are often used to distribute chlorine tablets throughout your pool. The problem is it is very easy for children to access chlorine tablets in your chlorine feeder.

So if your child opens up the feeder and swallows some of the tablets inside, it can result in a serious health consequence.

Slower acting

If your pool has issues that require a large quantity of chlorine to fix, such as yellow algae, it will take you many days to resolve the issue with chlorine tablets since they are slow acting.

Such an issue will be best treated using liquid chlorine or cal-hypo granular chlorine.

How much chlorine tablets to add to your swimming pool

How much tablets you need to add to your pool depends on many different factors, 

Assuming your pool’s pH, alkalinity, and cyanuric acid are at an optimal level, factors such as your pool’s size, the environment’s temperature, and how many people are frequently using the pool will all affect the chlorine requirement.


If you live in an area where you are exposed to strong sunlight, your chlorine will evaporate a lot faster. In contrast, a cooler temperature will extend your chlorine’s life.

In case your pool temperature increases by more than 10-degree F above 80-degree F, your chlorine demand can increase by more than 50%.

In other words, if you need 1.0 ppm chlorine to keep your pool sanitized at 80-degree F, your pool will need 1.5 ppm chlorine at 90-degree F to maintain the same level of sanitization.

The number of people using the pool

When more people are using the pool, your chlorine tablets will get used up more quickly since more organic matter is produced from people.

In case you host a pool party where you will see a large spike in chlorine demand, you may even consider chlorinating your pool with liquid chlorine since it works quicker.

Size of your pool

Bigger the size of your pool, the more chlorine tablets you will need to add. The following is a general recommendation for the chlorine tablet requirement for different sized pools.

Smaller pool

For a smaller pool with about 10 to 15,000 gallons of water,  you will want to use about one to two chlorine tablets per month in the off season. During the peak season, you will want to use around three to five tablets a week.

Larger sized pool

If you have a pool that contains around 15 to 25,000 gallons of water, you’ll want to use one to three tablets per month in the offseason. In the summertime, you will want to use anywhere between six to nine tablets per week.

That said, the best way to figure out your pool’s chlorine tablet requirement is to do consistent weekly testing.

If the test result shows that your pool is doing well in terms of chlorine level, you don’t need to worry about adding any more chlorine.

Otherwise, you will want to continue to add chlorine until your pool reaches an optimal chlorine level.

How long do chlorine tablets last in your pool?

How long your chlorine lasts does not depend on the size of your pool.

Your chlorine’s longevity depends on:

  1. The method you used to add chlorine tablets into your pool (feeder, skimmer, floater)
  2. The temperature of your pool. Chlorine tablets tend to last longer in a lower temperature
  3. The setting of your feeder or pump

Generally speaking, you can expect your tablets to dissolve in about two to three days fully.

How to choose the right chlorine tablets for your pool

Whichever chlorine tablet you use, there are no differences in the makeup of a chemical compound. However, there is a difference in the rate that different sized tablets dissolve.

1-inch chlorine tablets

1-inch chlorine tablets are suitable for small pools. It dissolves a lot faster than 3-inch tablets, so it raises the pH of your pool more quickly.

3-inch chlorine tablets

3-inch tablets are the cheapest in terms of the amount you get. You will likely need to use 3-inch tablets if you are currently using chlorine feeders since most chlorine feeders are made to fit 3-inch tablets.

One 3-inch tablet is capable of treating up to 10,000 gallons of water.

This is the most commonly used tablet size for pools. So, if you have a standard pool size, you would probably want to go with the 3-inch over 1-inch tablets.

Is liquid chlorine better?

Liquid chlorine is unstabilized, unlike chlorine tablets, which means it isn’t protected from UV rays. In other words, it doesn’t contain cyanuric acid nor any other elements. This can be good or bad, depending on your pool’s cyanuric acid needs.

Because liquid chlorine is already dissolved, it works at a more rapid rate than tablet forms. So if your pool needs to be treated with a large quantity of chlorine immediately, it’s a good idea to supplement with liquid chlorine on top of tablets.

One disadvantage of liquid chlorine is that it has a relatively short shelf-life compared to tablet forms. It will lose about half of its strength within six months of opening, and it will become largely ineffective after a year.

Different ways to add chlorine tablets to your pool

Automatic chlorinator

Using an automatic chlorinator is one of the most effective and convenient ways to add chlorine tablets into your pool.

Moreover, the equipment allows you to dispense chlorine at a set rate.

One downside of an automatic chlorinator is it can get quite pricey.

Floating chlorine dispenser

A floating dispenser does what its name suggests; it floats around the pool water distributing chlorine tablets throughout your pool.

You want to check every now and then to ensure your dispenser didn’t get stuck somewhere in your pool. Otherwise, you risk uneven distribution of chlorine.


You can also add chlorine tablets to your skimmer. It’s quick and easy with no hassle, and the water will carry dissolved chlorine throughout your pool.

What are the best chlorine tablets?

HTH 42033 Super 3-inch Chlorinating Tablets

This is currently by far the most popular chlorine tablet product on Amazon, with over 10,000 reviews. The product effectively sanitizes and protects your pool from harmful substances.

My favorite part of the product is that it is perfectly compatible to use with all types of equipment used to apply chlorine tablets, such as a floater, feeder, and skimmer.

The tablets are also safe to use for vinyl-lined pools and a pool with a saltwater system.

Furthermore, it helps to clarify your pool water so that you can enjoy your swim in clear water.

If you want to keep your pool clear of bacteria and algae for a long duration, then it’s hard to go wrong with this product.

A word of caution: Avoid adding the tablet directly into your pool, as this can potentially damage the pool surface.

Also, make sure your pool pump runs at least eight hours a day to help disperse the chlorine tablet throughout your pool.

Finally, you want to make sure your pool pH is at an ideal range of around 7.4. Otherwise, the chlorine sanitizer just won’t be as effective.

Because so many people have bought this product, you will inevitably find some unhappy customers. Some of the genuine complaints seem to be regarding tablets that were broken during delivery.

That said, there are equally as many reviews that show pictures of non-damaged tablets that appear perfectly fine.

In case you get a damaged product, you can always ship it back for free and receive a refund or another product, so this shouldn’t concern you too much.

Clorox XtraBlue 3-inch Long Lasting Chlorinating Tablets

This is another popular chlorine tablet product on Amazon with over 8,000 reviews. The tablets do what you’d expect them to do, such as killing bacteria and treating all types of pool algae. They are also effective for preventing stains, corrosion, and scales.

And thanks to its stabilized form, the tablet will last you a long time. Moreover, the product helps with keeping your water smooth since it contains a conditioner.

As with most chlorine tablets, these are easy to apply, and you only need to use them weekly to keep your pool chemical well-balanced.

The container comes with 10 tablets, which should last you a good few months.

But as with any chemical products, be sure to read the instructions carefully before use.

Most reviews are positive, and people seem to be especially happy about how long it lasts in their pools.

That said, you can also spot some reviews of people who are unhappy with its packaging because each chlorine tablet isn’t wrapped individually. But it is something that you can easily resolve by using any spare tongs in your house.

How to disperse chlorine tablets into your pool

You can disperse chlorine tablets into your pool in two ways.

One is using a chlorine floater in a residential setting. You can also use an inline chlorinator in a commercial setting.

You should avoid putting your chlorine tablets directly into your pool, skimmer, or pump basket. This will damage your pool equipment.

How to make sure chlorine works effectively in your pool

You need to ensure that your pool has a balanced pH. If not, your chlorine won’t be as effective.

You also want to make sure your pool has a low enough pH that hypochlorous ions are present in abundance.

Your pool cyanuric acid level plays an important role in improving the efficacy of chlorine as well. 

Cyanuric acid protects chlorine from the sun. Without it, your pool chlorine will gas off from the UV rays.

That said, too much cyanuric acid can also reduce chlorine’s efficacy, so it’s important you maintain a good balance.

Wrapped or unwrapped for chlorine tablets

Chlorine tablets can either come wrapped or unwrapped.

The idea behind wrapped tablets is that you can just drop them into a feeder or chlorinator from the wrap without you having to touch the tablet with your hand directly. Wrapped tablets usually cost more because of this seemingly extra protection for your hand.

In reality, it often does not protect your hand as well as you’d hope. You will still most likely get chlorine on your hands. There are also times you will have to adjust chlorine tablets inside the equipment after you add them.

If you are worried about protecting your hand, I’d recommend you use tongs to handle chlorine tablets.

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