What is residual chlorine? What is the standard residual chlorine concentration?

Definition of residual chlorine

Chlorine (chlorine) is a halogen element with a mass about 2.5 times larger than air. Water is only truly safe when it does not contain disease-causing microorganisms, and chlorine is used to destroy or inactivate them. Chlorine can be added to water as a gas, liquid, granular powder or tablet.

In swimming pools, the concept of residual chlorine refers to the remaining amount of chlorine that disinfects water and oxidizes organic substances, helping to immediately eliminate microorganisms such as bacteria, viruses, algae spores... as soon as they appear. Therefore, the level of residual chlorine is not only an important indicator to evaluate swimming pool quality, but also directly affects the health of users as well as the revenue of the business.

To accurately control residual chlorine concentration, the most effective, advanced and cost-effective method is to use a chlorine and fluoride meter.

What is the standard residual chlorine in a swimming pool?

According to experts, the ideal standard for swimming pool water quality is achieved when the residual chlorine concentration is between 0.6 and 1.5 mg/l (with a recommendation to maintain at 1–3 mg/l) and should be tested at least once a day. Within this threshold, swimming pool water is not only safe for users but also has the ability to effectively inhibit dangerous pathogens such as bacteria, algae, etc.

Based on the above standards, we can evaluate the water quality of the swimming pool to determine its safety and suitability for use. When using services or relaxing at areas with swimming pools to improve quality of life, everyone wants to be well cared for and absolutely safe. A green, clear, clean swimming pool is the highlight that helps businesses make a strong impression on customers.

The Risk When Chlorine Concentration In The Swimming Pool Exceeds The Limit

Recently, with the trend of using swimming pools becoming more and more popular in the summer, many businesses have expanded their scale to serve the entertainment needs of customers. However, not every place focuses on monitoring residual chlorine levels in water, leading to unwanted consequences. Maintaining proper chlorine levels is key to protecting user health and ensuring water quality.

When the chlorine level in the tank is lower than the required standard, the water will not be disinfectant enough, creating conditions for moss and bacteria to grow, such as Cryptosporidium - the main cause of diarrhea, or Chlamydia Trachomatis - the cause of conjunctivitis. On the contrary, if the chlorine concentration exceeds 3 mg/l, the risk of poisoning due to residual chlorine increases, causing symptoms of skin and eye irritation and other negative health effects.

Some studies show that pool lifeguards and professional swimmers often encounter health problems such as asthma and diseases related to the eyes, nose, and throat. This comes from frequent contact with swimming pool water with unbalanced residual chlorine content. If the residual chlorine level in the swimming pool is below the standard threshold, the disinfection ability will not be effective, creating conditions for microorganisms to grow and harm users.

On the contrary, when chlorine concentration exceeds the prescribed level, the irritating effects on the skin and respiratory system also become dangerous. Therefore, maintaining a stable and standard residual chlorine level is always a mandatory criterion for all swimming pool businesses, to ensure a safe and quality environment for customers - a factor that everyone always expects when using the service.

Treat substandard residual chlorine concentration in the swimming pool

When detecting that the residual chlorine level in the swimming pool is not within the standard range, whether it exceeds or is lower than the safe level, immediate adjustment measures are needed to protect users' health and ensure disinfection effectiveness. In case the residual chlorine level is too high, it should be reduced to the allowable level by using neutralizing agents, such as hydrogen peroxide. The amount of hydrogen peroxide used should be balanced based on the deviation of the chlorine concentration from the standard. 

If you discover that the residual chlorine level is too low, you can add additional chemicals in the form of chlorine powder or TCCA tablets to increase the chlorine concentration, thereby improving the disinfection ability of the pool water. Correct adjustment will help maintain the pool water in an optimal state, ensuring user safety and facilitating the effective disinfection process.

How to test chlorine concentration in water

Currently, there are many methods to test chlorine concentration in swimming pool water, such as using DPD test kits, OTO test kits or digital color meters. These methods have the advantage of low cost and ease of use, but the results are often only relative and the implementation process also takes a lot of time.

To overcome those limitations, the Chlorine and Fluoride meter was born to measure residual chlorine concentration in water and swimming pools quickly and with absolute accuracy. Through the data displayed on the screen, users can compare with the standard level to accurately determine whether the residual chlorine concentration is low or high, thereby taking appropriate adjustment measures to ensure the health of the user.

The HI701 low-range residual chlorine photometer has affirmed its position as the best-selling product in 2020 thanks to its advanced optical system, bringing maximum convenience to users. HI701 is compactly designed, with optimized function keys at the touch of a button, helping to perform measurement operations faster and more effectively than traditional methods. 

Furthermore, the automatic shut-off feature after 10 minutes contributes to improving safety and saving energy, which is one of the criteria highly appreciated by users. Currently, this product line has become the top choice of many swimming pool businesses, proving effective in controlling water quality..