Sodium Hypochlorite? (Liquid Chlorine) in Pools: All You Need to Know

Sodium Hypochlorite is an unstabilized, inorganic compound that comes in a liquid form. It has a chlorine availability of 10-12% and an active strength of 10-12%. When used in a 1% solution, it raises the pH to a level between 9 and 14.  Sodium hypochlorite (NaOCl) is a liquid solution containing approximately 15 percent chlorine. It is a liquid chlorine-releasing disinfectant commonly used to treat commercial pools. Sodium hypochlorite is widely used due to the ease of incorporating it in its liquid form and its relatively economical cost. Sodium hypochlorite (NaOCl) is a liquid chemical with CAS Number 7681529 and UN ID Number UN1791. It is not flammable and has a low level of instability. Sodium hypochlorite does not contain any stabilizer, and it does not increase the amount of cyanuric acid in 10,000 gallons of water. When introduced into pool or spa water, it reacts to raise the pH. When used in a pool or spa facility, the potency of the solution is characterized by an available chlorine content (ACC) of 10% to 12%, and a pH level ranging between 9 and 14. The pH must be corrected by the addition of an acidic material.

What is Hypochlorite?

Hypochlorite refers to any compound containing a metal ion and the (OCl-) anion. Hypochlorite most commonly refers to calcium, sodium, or lithium hypochlorite in pool usage. These compounds are often used as disinfectants in swimming pools due to their ability to effectively kill pathogens and algae.

Is Sodium Hypochlorite and Liquid Chlorine the same?

Yes, sodium hypochlorite and liquid chlorine are the same. Sodium hypochlorite (NaOCl) is also known as liquid chlorine. It is a liquid solution that contains chlorine and is commonly used to treat commercial pools.

How much Chlorine is in Liquid Chlorine?

Liquid chlorine contains 8%, 10%, or 12.5% available chlorine. One gallon of liquid chlorine (12%) contains about one pound of pure chlorine.

What are the Physical Properties of Sodium Hypochlorite?

Sodium hypochlorite is available in two concentrations: 10% and 12%. The 10% solution weighs 9.50 lbs/gal and increases TDS by 0.83 lbs/gal in 10,000 gallons of water. The 12% solution weighs 9.74 lbs/gal and increases TDS by 1.00 lbs/gal. Both solutions have a pH of 13.0 and a shelf life of 60 days.

How Stable is Sodium Hypochlorite?

Sodium hypochlorite has the potential to lose a significant amount of available chlorine within a short span of days. The stability of sodium hypochlorite is strongly affected by sunlight, heat, pH, and the presence of heavy metals. The higher the chlorine concentration or temperature, the faster the deterioration. Iron, copper, nickel, or cobalt enhance the likelihood of catalyzing this deterioration, with iron posing the most significant issue. Even a small amount of iron increases the chance of rapid deterioration of sodium hypochlorite solutions. Iron contamination comes from the caustic soda used in manufacturing. If the iron concentration in the solution is only 0.5 ppm, it rapidly deteriorates within a few days. The most stable sodium hypochlorite solution is 10 percent with a pH of 11.0 and iron, copper, nickel, and cobalt below 0.5 ppm. Sodium hypochlorite should be stored in a dark room at about 70° F (20° C).

What is the Half-Life of Sodium Hypochlorite?

The half-life of a substance refers to the time it takes for half of it to degrade. For a 10% sodium hypochlorite solution stored at 77° F, the half-life is 220 days. This means it will degrade to 5% strength in this time.

How Quickly Does Liquid Chlorine Lose Its Strength?

Liquid chlorine degrades rapidly due to its instability according to the Handbook of Chlorination, 4th Edition, Geo. C. White published in 1999. The degradation rate increases with higher chlorine concentrations and temperatures. The presence of metals like iron, copper, nickel, or cobalt also accelerates this process. Iron, even in small amounts, causes rapid deterioration of sodium hypochlorite, especially if it contaminates the caustic soda used in manufacturing. The most stable sodium hypochlorite solution is 10.0% with a pH of 11.0, not 12.5% with a pH of 13. Liquid chlorine should be stored in a dark room at 70° F (20° C). The table below shows the degradation of 10% and 12% sodium hypochlorite solutions over time.

What is the Liquid Chlorine Degradation Table?

The “Liquid Chlorine Degradation Table” is a table that shows the degradation rate of liquid chlorine (sodium hypochlorite) over time. It provides information on the percentage of available chlorine remaining in 12% and 10% sodium hypochlorite solutions at different time intervals. The Liquid Chlorine Degradation Table is as follows:

Days	12% Sodium Hypochlorite	10% Sodium Hypochlorite
10	11.5	9.7
20	11	9
30	9.7	8.7
40	8.8	8.5
60	6.2	8
90	4.7	7.2

How Can You Test the Strength of Sodium Hypochlorite?

There are test kits available for measuring the concentration of sodium hypochlorite. These include: Taylor Technologies’ Chlorine (Bleach) Test #K-1579 LaMotte Company’s Chlorine Model LB, Code 7894 Hach Hypochlorite Test Kit Model CN-HRDT. These kits ensure the maintained strength of the utilized or distributed sodium hypochlorite.

Where is Sodium Hypochlorite used?

Sodium hypochlorite is used in commercial pools and spas. Sodium hypochlorite is a commonly utilized disinfectant for these facilities due to the ease of dispensing it in a liquid state and its relatively low cost. When introduced into pool or spa water, sodium hypochlorite reacts to raise the pH. The strength when used at the pool or spa facility is 10% to 12% available chlorine content (ACC) with a pH between 9 and 14. The pH must be corrected by the addition of an acidic material. Sodium hypochlorite is also used in residential applications and small pools when the facility is closed to bathers. Sodium hypochlorite is safe to use in white plaster, colored plaster, vinyl liner, fiberglass, acrylic, and painted pools.

How is Sodium Hypochlorite Used?

Sodium hypochlorite is used for regular chlorination and superchlorination. Sodium hypochlorite provides 10 ppm and 12 ppm FAC (Free Available Chlorine) respectively when 1 gallon is added to 10,000 gallons of water. The amount required to increase FAC by 1 ppm in 10,000 gallons is 12.8 fl. oz. for the 10% solution and 10.6 fl. oz. for the 12% solution.

How to increase Chlorine in the pool with Sodium Hypochlorite?

Increasing the chlorine level in the pool with sodium hypochlorite is achieved by using a formula to calculate the amount of chlorine needed. First, the desired increase in parts per million (ppm) of chlorine in the pool is determined. Following this, the pool’s volume in gallons is divided by 10,000. The chlorine dosage table is then consulted to identify the amount of chlorine required to elevate the chlorine level by 1 ppm. The values obtained from these steps are multiplied to yield the total amount of chlorine necessary. For example, for an 18,500-gallon pool where the aim is to elevate the chlorine level by 3 ppm using 12.5% sodium hypochlorite, approximately 2 quarts or ½ gallon would be required. Sodium Hypochlorite is usually introduced into commercial pools and spas using displacement feeder pumps. Manual addition is common in residential applications and several small pools when the facility is closed to bathers. The usual pH correction with muriatic acid involves using between 10 and 16 fluid ounces for every one gallon of sodium hypochlorite. Sodium hypochlorite is applied by pouring or pumping. Sodium hypochlorite initially raises the pH due to the presence of hydroxide. However, as HOCl degrades, it produces HCl, which reduces the pH. The net pH effect is near zero.

What Happens When Sodium Hypochlorite is Added to Water?

When sodium hypochlorite is added to water, it produces hypochlorous acid and a by-product: NaOCl + H2O → HOCl + Na+ + OH– . The hypochlorous acid then dissociates into a hydrogen ion and a hypochlorite ion: HOCl → H+ + OCl– . When added to water, compounds of sodium hypochlorite generate hypochlorous acid by releasing the sodium ion and acquiring a hydrogen ion. The only distinction between the reactions of any hypochlorite and chlorine gas is the side reaction.

How does Sodium Hypochlorite affect TDS?

Sodium hypochlorite affects TDS by introducing into the water inert ingredients, including a substantial amount of salt (NaCl) and some amount of sodium hydroxide. After reacting with contaminants in the water, sodium hypochlorite leaves behind a chloride ion (Cl) and sodium ion (Na), non-volatile substances that are only eliminated when water is removed from the pool. These ions build up as TDS over time.

What are the Benefits of Sodium Hypochlorite?

Sodium hypochlorite acts as a primary sanitizer and disinfectant, killing all living microorganisms and disease-causing organisms. Sodium hypochlorite also serves as an oxidizer, destroying ammonia and swimmer waste, and as an algaecide, killing algae. Sodium hypochlorite provides a lasting residual effect.

How to store Sodium Hypochlorite?

Sodium hypochlorite has to be stored in a cool, dark environment. Sodium hypochlorite also has to be stored in a vented container due to its gassing off. The container has to be kept in a cool, dry, well-ventilated place. The most stable sodium hypochlorite solution is 10 percent with a pH of 11.0 and iron, copper, nickel, and cobalt below 0.5 ppm. It should be stored in a dark room at about 70° F (20° C).

How is Sodium Hypochlorite Sold?

Sodium hypochlorite is sold in various concentrations. Pool stores sell sodium hypochlorite, also known as liquid chlorine, in 10% and 12.5% concentrations. Grocery stores, home centers, and big box retailers typically sell sodium hypochlorite as bleach in 5.25%, 6%, and 8% concentrations. Sodium hypochlorite, also known as liquid chlorine, is a liquid solution that contains approximately 15 percent chlorine. It is available in two concentrations: 10% and 12%. The strength when used at the pool or spa facility is 10% to 12% available chlorine content (ACC) with a pH between 9 and 14. Sodium hypochlorite typically contains 8%, 10%, or 12.5% available chlorine and does not include a stabilizer such as cyanuric acid. While sodium hypochlorite has the ability to be produced with a chlorine concentration up to 15%, this condition is unstable and rapidly converts into gas. Therefore, sodium hypochlorite is usually produced with a concentration of around 12.5%, with most manufacturers guaranteeing a minimum of 12%. It is even more stable at 10%, and in some regions, 10% sodium hypochlorite is produced and sold.