With an understanding of galvanic corrosion, stains in salt-chlorine pools don\u2019t have to be a mystery.<\/p>\n
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| Salt \u00a0 chlorine pools have become popular over the past few years. There are no \u00a0 hazardous chemicals on site, and water is sanitized and oxidized \u00a0 automatically. Also, there are little to no chloramines. And many users of \u00a0 salt generators claim softer-feeling water with less chemical odor and no dry \u00a0 or irritated skin.<\/p>\n Yet \u00a0 in spite of all these benefits, some have also reported strange phenomena. \u00a0 These include discolored water and unusual stains that are hard to remove and \u00a0 prevent.<\/p>\n Stains \u00a0 appearing in salt pools include: While \u00a0 these stains seem to be a mystery, typically they are a result of the high \u00a0 TDS in salt pools and a simple chemical reaction known as galvanic corrosion.<\/p>\n To \u00a0 understand this electro-chemical reaction, a simple grasp of the technology \u00a0 of chlorine generators is first needed.<\/p>\n Salt \u00a0 chlorine<\/span><\/strong><\/p>\n Chlorine \u00a0 generators work through a process known as electrolysis.<\/p>\n In \u00a0 nature, chlorine is found primarily in the chloride ion, a component of salt \u00a0 found in the earth or the oceans. Electrolysis is the means of generating \u00a0 chemical products from their native state. A salt generator works by passing \u00a0 electricity through a solution of sodium chloride to produce chlorine as a \u00a0 disinfectant or sanitizer. The most commonly used chlorine generators are the \u00a0 in-line type. In these systems, salt water is circulated over electrochemical \u00a0 cells. The cells used in these systems typically are made of titanium, and \u00a0 they convert the sodium chloride to free available chlorine. Now it\u2019s \u00a0 important to understand how this metal relates to galvanic corrosion.<\/p>\n Galvanic \u00a0 corrosion<\/span><\/strong> Some metals are nobler and more cathodic, meaning positive currents flow from \u00a0 them. They also tend to steal electrons from the less noble anodic or \u00a0 negative metals. A galvanic corrosion chart is used in industries that work \u00a0 with fluids and metals, such as cooling towers. The chart shows that the \u00a0 \u201canodic\u201d or \u201cless noble\u201d metals at the negative end of the series \u2014 such as \u00a0 magnesium, zinc and aluminum \u2014 are more likely to corrode than those at the \u00a0 \u201ccathodic\u201d or \u201cnoble\u201d end, which include gold and graphite.<\/p>\n There \u00a0 are three things needed in order for galvanic corrosion to occur: In \u00a0 a swimming pool, all three of these exist due to high TDS from the salt \u00a0 content of the water. Most pools contain some copper in the system as well as \u00a0 in the heat exchanger, or in any brass fittings or pipe that may be in the \u00a0 hydraulics. As discussed earlier, the electrochemical cells in most chlorine \u00a0 generators are made of titanium. Copper is a less noble metal than titanium, \u00a0 and thus it corrodes as a result of the electrolysis in the high salt \u00a0 solution.<\/p>\n This \u00a0 electrolysis leaves black stains and debris in the pool. The copper also is \u00a0 rendered insoluble in the water, which may create a green translucent color.<\/p>\n Solutions \u00a0 to staining<\/span><\/strong> However, \u00a0 the addition of zinc in these types of systems can prevent corrosion and stop \u00a0 staining. Zinc is very low on the galvanic chart, and is one of the most \u00a0 anodic metals found. In salt chlorine pools, zinc can be added as a solid \u00a0 weight into the skimmer or attached in the circulation system. This slows or \u00a0 stops the corrosion of copper. If the water is discolored from copper, it is \u00a0 recommended to use a metal-removal product along with the zinc. This removes \u00a0 the current discoloration and prevents reoccurrence. Most metal products on \u00a0 the market tend to be phosphate-based, and this too can cause problems in a \u00a0 salt chlorine generator. When selecting a metal product, make sure it\u2019s \u00a0 phosphate-free.<\/p>\n Another \u00a0 mystery in both salt and regular pools is the occurrence of a strange purple \u00a0 coloring and debris. This is due to high levels of cyanuric acid and \u00a0 insoluble copper in the water. If pH and alkalinity drop too low, copper \u00a0 cyanurate is formed, leaving a purple residue along the water line, and \u00a0 around lights and steps. The solution here is to lower cyanuric acid down to \u00a0 35ppm to 50ppm, and adjust up the alkalinity and pH. Also, the addition of \u00a0 zinc will help keep copper from corroding into the water.<\/p>\n These \u00a0 simple methods should help solve the mystery…and remove the stains.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Source: Terry Arko- Pool and Spa News | 8.14.2009<\/strong><\/p>\n","protected":false},"excerpt":{"rendered":" With an understanding of galvanic corrosion, stains in salt-chlorine pools don\u2019t have to be a mystery. Salt \u00a0 chlorine pools have become popular over the past few years. There are no \u00a0 hazardous chemicals on site, and water is … Continue reading |