Chlorine Generation in Pools: All You Need to Know

Chlorine generation is the process of producing chlorine gas, typically through electrolysis. This involves using a chlorine generator that uses resources like salt, electricity, and water. The generator has a plastic tank divided into two compartments by a filter-type membrane. When electricity separates chlorine from sodium in the salt solution compartment, chlorine gas is generated. This gas then mixes with fresh water in the smaller chamber to form sodium hydroxide. The chlorine gas is then injected into the circulation plumbing. Some generators produce chlorine directly in the circulation water flow for direct application to the pool or spa water.

How do Chlorine Generators Work?

Chlorine generators work by using resources like salt, electricity, and water to produce chlorine gas through electrolysis. They have a plastic tank divided into two compartments by a filter-type membrane. The larger compartment, containing a positively charged electrode (anode), is filled with a salt (sodium chloride) and water solution. The smaller compartment, with a negatively charged electrode (cathode), contains distilled or municipal water. When electricity separates chlorine from sodium in the salt solution compartment, chlorine gas is generated. This gas rises, mixes with fresh water in the smaller chamber to form sodium hydroxide, which is drained periodically. The chlorine gas is then injected into the circulation plumbing. The electrical current is supplied through a transformer that converts 110- or 220-volt AC into 12-volt DC. Regulating the current controls the volume of chlorine produced. Some generators produce chlorine directly in the circulation water flow for direct application to the pool or spa water.

What are Salt Water Generators(SWGs)?

Salt chlorine generators are devices that convert salt into chlorine, maintaining a chlorinated pool. They work by adding ordinary table salt to the pool water and through an electrolytic process, they convert the salt into chlorine. These generators are increasingly common and are a cost-effective way to sanitize large pools or spas. They use inexpensive resources like salt, electricity, and water to produce chlorine gas. Users report that the increased salinity gives the water a silky texture and reduces chlorine odors. However, maintaining a good water balance and a clean pool is key to eliminating odors. Salt Water Generators(SWGs) are essentially miniature chlorine factories. They function similarly to large-scale chlorine plants, but use a set of permanent electrodes, typically made of titanium plated with ruthenium. These electrodes are expected to last three to five years.

How Does a Salt Water Chlorine Generator Work?

A Salt Water Chlorine Generator (SWG) creates chlorine from salt. When electricity passes through a salt and water solution (brine), it produces hydrogen gas at the negative electrode, sodium hydroxide at the negative electrode, and chlorine gas at the positive electrode. The chemical reaction can be summarized as follows: salt + water yields chlorine (gas) + sodium hydroxide + hydrogen (gas). This process ideally produces pure hydrogen gas, pure chlorine gas, and pure sodium hydroxide. In more detail, the generator has a plastic tank divided into two compartments by a filter-type membrane. The larger compartment, containing a positively charged electrode (anode), is filled with a salt (sodium chloride) and water solution. The smaller compartment, with a negatively charged electrode (cathode), contains distilled or municipal water. The membrane allows electricity to pass but restricts the chemicals to one side. Chlorine gas is generated in the salt solution compartment when electricity separates chlorine from sodium. The gas rises, mixes with fresh water in the smaller chamber to form sodium hydroxide, which is drained periodically. Hydrogen gas formed is vented out. Salt is added periodically to recharge the system. The chlorine gas is then injected into the circulation plumbing. The electrical current is supplied through a transformer that converts 110- or 220-volt AC into 12-volt DC. Regulating the current controls the volume of chlorine produced. Some generators produce chlorine directly in the circulation water flow for direct application to the pool or spa water.

How does an In-line Salt Water Generator (SWG) work?

An In-line Salt Water Generator (SWG) operates by allowing salted pool water to flow through an SWG cell. Direct current (DC) electricity is then applied to the plates within this cell. This triggers an electrolysis reaction, producing chlorine gas, caustic soda, and hydrogen gas. These products are not separated but introduced into the pool water flow. The electrolysis occurs in an electrolytic cell installed in the plumbing line in the recirculation system. The cell contains layers of plates charged with DC electricity, provided by a separate power supply or controller unit. For the unit to operate efficiently, a salt concentration of 3,000 to 3,500 parts per million (ppm) is needed.

How Does an In-line System Work?

An In-line system works by producing chlorine directly in the pool from salt added to the pool water. The electrolysis occurs in an electrolytic cell installed in the plumbing line in the recirculation system. The cell contains layers of plates charged with DC electricity, provided by a separate power supply or controller unit. For the unit to operate efficiently, a salt concentration of 3,000 to 3,500 parts per million (ppm) is needed. This equates to adding 250 to 300 pounds of salt per 10,000 gallons of water. As pool water, salted, flows through an in-line cell, direct current (DC) electricity is applied to the cell plates. This triggers an electrolysis reaction, producing chlorine gas, caustic soda, and hydrogen gas. These products are not separated but introduced into the pool water flow. To prevent scale buildup on the plates, many in-line systems periodically reverse the electrical charge on the plates. This process removes any accumulated calcium or magnesium but reduces the plates’ lifespan.

How does an In-line SWG prevent scale buildup?

To prevent scale buildup on the SWG plates, many SWGs periodically reverse the electrical charge on the plates. This process removes any accumulated calcium or magnesium but reduces the plates’ lifespan.

Does an In-line SWG change the water’s pH

In theory, in-line SWGs do not alter the water’s pH. This is because the neutral salt (NaCl) is split into sodium and chlorine and reintroduced into the water. However, the hydrogen gas produced in a chlorine generator pool escapes, leaving behind hydroxide that raises the pH. Additionally, the chlorine gas produced by the SWG creates hydrochloric acid and hypochlorous acid. The caustic soda neutralizes the hydrochloric acid, and the escaping hydrogen gas creates turbulence, raising the pH.

What is the Process of Water Chemistry in Salt Chlorine Generators?

Salt chlorine generators require a salt concentration of 379 parts per million, compared to ocean water’s 38,000 parts per million. The salt concentration can be tested using a kit that comes with the generator or the kit has to be purchased from a pool supply store. The generator’s computerized control unit converts household AC current (120 or 240 volts) to low-voltage DC current. This current is sent into an electrolytic cell mounted in a plumbing fitting, which is added to the pool plumbing after the heater. Chlorine is produced as the salted pool water passes between the electrodes. Chlorine production has to be adjusted by changing the control settings or the generator’s operating hours. Salt has the potential to be corrosive and tends to build up on surfaces. Therefore, salt chlorine generators usually self-clean every few hours. Most units have sensors to measure the system’s flow rate and shut down the unit if problems are detected.

How Much Chlorine is Produced by Residential Salt Water Generators (SWGs)?

Residential Salt Water Generators (SWGs) designed for pools up to 25,000 gallons have the potential to produce about 1 pound of pure chlorine per day if run continuously at 100%. If run for 8 hours at 70%, they produce about 5 or 6 ounces of pure chlorine. This production rate applies to both brine and in-line systems. The chlorine produced by these systems is identical to the type already used in the pool and is measured with standard test kits or strips. However, the actual output of the SWG, or the amount of chlorine produced, is based on running the SWG 24 hours a day. For a residential pool that only operates the filtration pump for 8 hours or less, this means the SWG is too small for the pump run time.

Is a Salt Water Generator (SWG) preferable to liquid chlorine?

The preference between a Salt Water Generator (SWG) and liquid chlorine depends on several factors. While it’s cheaper to produce chlorine in the pool with a SWG than to buy liquid chlorine, a SWG continually increases the pool’s pH, requiring acid that lowers total alkalinity. A SWG provides a constant daily chlorine amount, maintaining a steady chlorine level, whereas liquid chlorine creates high levels that decrease over time, resulting in peaks and troughs. Each situation requires individual analysis.

Why Does pH Increase with Salt Water Generators (SWGs)?

The pH increases with Salt Water Generators (SWGs) because the electrolysis of salt water with an SWG produces chlorine gas and sodium hydroxide. The sodium hydroxide, along with hydrogen gas, increases the pH level. This is because the hydrogen gas, which is not soluble in water, escapes to the atmosphere, causing turbulence and raising the pH.

How does a Salt Water Generator (SWG) affect TDS?

An SWG pool adds 3,400 ppm of salt to the normal TDS, which may be 1,000-2,500 ppm. This makes the total TDS around 4,000 to 6,000 ppm. Pool water with this TDS concentration conducts electricity well, turning the pool into a low voltage battery.

What are the Advantages of Installing a Chlorine Generator?

Installing a chlorine generator reduces chemical costs and improves water quality by providing continuous chlorination. Salt Water Generators (SWGs) superchlorinate the water, reducing the need for separate superchlorination. They also eliminate the need for hazardous chemical transportation, storage, and handling, as well as related safety training and permits.

What are the Disadvantages of Using a Chlorine Generator?

Like any device, SWGs are subject to breakdowns and require maintenance and repairs. They produce a fixed amount of chlorine, which is not sufficient to handle a sudden increase in organic load from a large number of swimmers. Recovery time tends to be lengthy, and it is possible that additional chlorine needs to be added separately for residential pools.

What are the Costs Associated with a Chlorine Generator?

There are four main costs associated with a chlorine generator: The cost of the unit itself, which typically ranges from 200$ to 1,000$. The cost of installation, which varies depending on the complexity of the plumbing required. The cost of salt for a residential brine system is calculated at eleven cents per pound, which  leads to an annual expense ranging from 9 to 22$. The cost of the electricity to run the unit.

What are the Best Practices for Using Salt Chlorine Generators?

The best practices for using salt chlorine generators include adding salt to the pool by broadcasting it over the pool when the circulation is running and not through the skimmer. Granulated, table-quality salt is preferably to be used. Before starting the generator, the pool has to be brushed and the water circulated for 24 hours to completely dissolve the salt. The generator has to be started at a 50% production level and the chlorine level checked the next day. The residual has to be between 1 and 3 ppm. The generator’s production level has to be adjusted as needed. Every two months, the electrolytic cell has to be removed and the scale cleaned off the electrodes. When adding acid or soda ash to prevent reactions with the electrodes, the generator has to be turned off. Normal operations are resumed after the acid or soda ash has been thoroughly distributed throughout the pool water.