By Terry Arko
Saltwater systems have become extremely popular over the past five to 10 years. The system’s popularity, however, began with pools, to improve the swimming experience while simultaneously reducing the amount of traditional chemicals needed to sanitize the water. Add to this the safety benefit of eliminating the need to store large quantities of chlorine on-site.
Now that salt chlorine generators are universally accepted and proven to work wonders on pools, the technology has expanded to include systems for hot tubs. This water treatment system makes a lot of sense for smaller bodies of water, such as a hot tub as users prefer to soak in the water for health and relaxation and are not interested in immersing themselves in a tub of chemicals.
As retailers and service professionals encounter salt chlorine generators on hot tubs more frequently, it is important to understand how these systems work and how they differ from those systems used on pools. With this knowledge, the industry will be better prepared to service these hot tubs and pro-actively deal with issues that arise from the use of salt chlorine generators.
What is a salt system?
First, it is important to understand how salt chlorine generators work and how this method of water treatment is applied to pools and hot tubs.
Salt systems use a method known as electrolysis, which splits atoms of molecules apart in solution to create active chemicals. The chemicals produced are based on what the molecule is in the solution. In 1800, two scientists discovered the water molecule H2O could be split into active oxygen (O) and hydrogen (H) through electrolysis. Electrolysis has been used in treating drinking water and wastewater since the early 1900s. Recently, the process of splitting salt molecules to create active sanitizer in hot tubs has taken off. The two most common molecules for hot tub water treatment are sodium chloride (NaCl) and sodium bromide (NaBr). These two halogen salts are split by electrolysis to create active chlorine (Cl) or bromine (Br).
How does it work in a hot tub?
Salt generators work to produce active sanitizer in water. The term ‘salt system’ is a misnomer as it leads to the conclusion this is a non-chemical system. In fact, saltwater is part of a process to produce active sanitizer. Sanitizers are needed (required) in hot tubs to disinfect against pathogenic bacteria and viruses present in water as a result of bather use. Effective sanitizers for hot tubs will act to sanitize, oxidize, and leave a small residual behind in the water. The two most common and effective sanitizers for this purpose are chlorine and bromine, which are both categorized as halogens. This means they are created from inert salts and, after they have reacted in water, they return to salts again.The word halogen comes from the Greek words meaning ‘salt-former.’ Most salt generator systems work by taking a simple solution of either sodium chloride or sodium bromide that is circulated through a device with two cells made of a noble metal—platinum or titanium are two of the most commonly used. A low-voltage electrical charge is introduced through the cells. One cell is defined as an anode with positive charges, while the other is known as the cathode with negative charges. Chloride (Cl−) is a negative-charged atom that bonds to the positive-charged sodium (Na) atom (Cl−+ NA+= NaCl).
In solution, the negative-charged Cl atom is pulled toward the positive-charged anode and the positive-charged Na atom is pulled to the negative-charged cathode. After which the molecule is split. At the anode, the chloride is oxidized to chlorine. Sodium is pulled towards the negative-charged cathode where hydrogen is being created. The atoms of Cl and Na rejoin after this process to once again form NaCl sodium chloride.
As long as the NaCl sodium chloride molecules are present in the water, the reaction of creating active chlorine is continuous. Bromine is created the same way. NaBr sodium bromide in solution passes by the anode and cathode. At the positive-charged anode, bromide is oxidized to active bromine, while at the negative-charged cathode, sodium hydroxide (NaOH) is created. The positively charged anode of a salt generator always produces oxygen, which acts to oxidize either chloride or bromide. As these units also produce oxygen, there is increased oxidation, which breaks up combined chlorine and helps to reduce waste. Increased oxygen leads to better water quality and less draining. At the cathode, hydrogen is created. Sodium mixes with water and hydrogen to create sodium hydroxide along with some hydrogen gas.