Why Do People Put Chlorine In Pools?

What the main chemical that makes a pool crystal clear and safe for swimming? It's the mighty Chlorine. But why do people put it in their pools, and how does it actually work? Let's find out.

The Need for Chlorine

Chlorine's role in pool is ensure a safe environment for swimmers. Like every water body, pool is highly susceptible to contaminants like sweat, dirt, dead leaves, parasites and bugs. More critically, they also include microorganisms like bacteria and viruses, which can thrive in warm pool water.

The Role of Chlorine

Chlorine is an effective disinfectant for pools due to its ability to kill bacteria and control the growth of algae. Here's how it works:

  1. Disinfection: When chlorine is added to pool water, it forms hypochlorous acid and hypochlorite ions. These two compounds actively destroy bacteria and viruses by attacking their cell walls and disrupting their enzymes.

  2. Oxidation: Chlorine also acts as a powerful oxidizing agent. It breaks down or "burns up" organic materials, removing contaminants and keeping the water clear.

  3. Residual Protection: Although there are many disinfectants in the market, only Chlorine lasts multiple hours. As long as you have residual level, it will guard against future contamination. This helps maintain a sanitary pool environment.

Types of Pool Chlorine

Pool owners can choose from various forms of chlorine to suit their needs:

  1. Liquid Chlorine: Easy to use but requires frequent dosing. This is also known as Sodium Hypochlorite.
  2. Chlorine Tablets: Slow-dissolving tablets that provide continuous protection.
  3. Chlorine Powder/Granules: A quick way to increase chlorine levels as needed. 
  4. Salt Chlorinators: These systems generate chlorine from salt, reducing the need for manual dosing.

    Chlorine Tablets, and powder/granules are available in both 70% and 90% concentration. Although there is no such thing as 90% Chlorine, it's the term used in swimming pool market. 90% Chlorine Is simply 70% Chlorine with Cyanuric Acid.

Be Careful with Chlorine

While chlorine is crucial for pool sanitization, it must be used carefully. Too much chlorine can lead to formation of chloramines, which cause skin and eye irritation, and that distinct "pool smell". On the other hand, too little chlorine can result in poor pool sanitation. 

How Much Chlorine to Use?

ANSI recommends that chlorine concentration should be between 3-5ppm. But if you want to use Chlorine as an algae preventer as well, then I recommend the following concentration:

If the pool is Indoor, chlorine concentration should go exceed 2ppm.

If the pool is outdoor, follow the table below. (Please note that these are my dosages and are not recommended by ANSI. Rather, this dosage helps disinfect and prevent algae in the pool)

Note: If you're using Spark Pool Conditioner in your outdoor pool, you can use just 2ppm of 90% Chlorine for disinfection.

How to Protect Chlorine In Outdoor Pools

Sunlight can destroy chlorine completely within hours. That's why many pool owners use Cyanuric Acid. This acid creates a weak bond with Free Chlorine, and breaks slowly to disinfect the pool for longer period of time. If you want constant protection of chlorine from sunlight, while having 100% killing action, use Active Summer Pool Protector instead. Click here to read more.


Chlorine disinfects and sanitizes the pool. If used properly, it's the only chemical that disinfects for a very long period of time. Chlorine is safe, cheap, and readily available chemical in the market. No wonder it is the most used disinfectant for pool.

Thank you for your attention.


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