Salt chlorine generators

by Sally Bouorm | December 1, 2010 3:11 pm

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By Terry Arko

As salt water pools become more popular in both residential and commercial pool installations, issues with salt chlorine generators have also been garnering more attention.

In a pool setting, salt generators produce hydrogen (H) and chlorine (Cl₂) gas, and a solution of sodium hydroxide (NaOH). When salt generators are working properly, they continuously produce free available chlorine (FAC) to proper set levels. However, when they fail, there will not be enough free chlorine to keep up with demand. While failure can be caused by several factors, this article will focus on one: high phosphate levels.

How salt chlorine generators work

The technology behind salt chlorine generators goes back to the 1800s, when scientists first developed electrolysis, a process that involves electric current being passed through a substance to elicit a chemical change.

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In the case of salt chlorine generators, salts (e.g. sodium chloride [NaCl] or sodium bromide [NaBr]), are used in a solution that is subjected to a low-voltage electrical current. The current flows between a pair of electrodes with opposing charges—the anode, which is positively charged, and the cathode, which is negatively charged. Electrical ions flow back and forth between the two electrodes; when the salt passes across them, molecules are split. Chlorine gas is produced at the anode, while hydrogen gas is produced at the cathode.

There are numerous reasons for salt chlorine generator failure, including dirty or calcified electrodes, lack of power to electrodes and/or insufficient salt levels in the water. There is, however, one primary factor to consider when a salt chlorine generator fails—the presence of phosphates in the pool water.

The phosphate connection

When phosphate levels exceed 500 parts per billion (ppb), the salt chlorine generator may cease to produce enough FAC to keep up with demand. In fact, most manufacturers recommend a phosphate test when there is a problem with production of FAC. If phosphate levels are near or over 500 ppb, a phosphate removal treatment is advised. This can help salt chlorine generators function as they intended.

High phosphate levels are directly linked to industrial uses of orthophosphate in water treatment. Orthophosphates are detrimental to salt chlorine generators, as they serve as nutrients for algae; they can contribute to scale, in both traditional and salt water pools. Zinc (Zn) orthophosphate is used in drinking water systems because it adheres to metal pipes and acts as an anti-corrosion agent.

The real interference of phosphates in chlorine generators is still somewhat theoretical. However, it appears that since orthophosphates attach to metals and are anodic or negative ions they could attach to the anode and cause an interference with the flow of electrons between the anode and the cathode of the salt chlorine generator. Another theory is that since algae spores feed on nutrients such as phosphate and begin to bloom, chlorine is consumed at higher levels. More work research needs to be performed to define the exact cause of interference from orthophosphates. Regardless of the mechanisms involved, it is clear that higher orthophosphate levels seem to cause interference with the normal operation of the salt chlorine generators.

Where are the phosphates coming from?

Phosphates can be introduced into swimming pool water via a multitude of sources, including fertilizers, organic debris, soil, detergents/cleaners, tile cleaners and metal-sequestering chemicals. It can also be deposited through human perspiration and urea (NH₂) ₂CO.

There are several different forms of phosphate, depending on the source; however, eventually it becomes a form of orthophosphate. Metal products are one of the main culprits that cause failure in salt chlorine generators. This is because staining from metals is more prevalent in salt chlorine pools, due to potential galvanic corrosion from the high total dissolved solids (TDS) of the salt and dissimilar metals present in the water.

As a result, most salt chlorine generator manufacturers recommend using a metal-sequestering agent. However, many of these products use phosphonic (C-PO[OR]₂) or phosphoric-acid (H₃PO₄)-based formulas. When added to a salt pool, they will break down the phosphate to free orthophosphate, which causes problems with the chlorine generator electrodes. As such, it is best to use a phosphate-free metal sequestering product.

Removing the phosphates

Phosphates can be easily removed from pool water by using a phosphate remover. Orthophosphates in pool water exist in a soluble form; the most effective phosphate removers work by turning soluble orthophosphate precipitate into a solid. This will cause some water cloudiness, which can be readily filtered out with a clarifier. However, keep in mind that the more phosphate used, the cloudier the water will become. In extreme cases, it can take up to two to three days for the cloudiness to clear completely. During this cloudy period, it is important to turn off the salt chlorine generator; liquid chlorine can be used in the interim to keep the residual up.

The other option for extreme phosphate levels (e.g. near or more than 5,000 ppb) is to drain and dilute some or all of the water. This method may be better used for commercial pools, where shut down time is limited and cloudiness of the water is regulated. In these cases, it is advisable to dilute out as much phosphate as possible and use maintenance doses of phosphate remover to manage levels.

Pre-emptive phosphate maintenance

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Commercial pool operators should avoid using any phosphate-based cleaners for decking or tiles. Operators of any seasonal outdoor pools located near lakes should discourage patrons from visiting the pool after swimming in a lake (at the very least, thorough showering before entering the pool should be mandatory).

In the case of residential pools, care should be taken when fertilizing any grass or plants near the pool area. Source water should be tested regularly for phosphates as well. Many municipalities treat water with straight orthophosphates at different times. If this is the case, phosphate treatment is recommended when filling or topping off the pool.

The method for winterizing a salt chlorine generator pool is not that different from a regular pool. In areas where winter is extreme and a hard shut down is required, the water level in the pool should be lowered, with winterizing chemicals added as usual. The salt chlorine generator itself should be deactivated and, in some cases, disassembled and stored; in some areas, a complete shut down may not be necessary. Check with the manufacturer for specific winterizing instructions.

Understanding a pool’s underlying water chemistry is vital if a salt chlorine generator is to operate properly. In a salt water pool, keeping the phosphates low is the secret to letting the free chlorine flow.

PHOSPHATE REMOVAL: A CANADIAN TEST CASE

Kathryn Pollock of Pollock Pools & Spas in Guelph, Ont., found the excessive rains experienced in her area over the course of two summers have caused a much higher level of phosphates in all their customers’ pools. “The way I understand it, phosphates are airborne and the rain pulls them down into the pool water,” she explains. “They are also introduced from fertilizers used by farmers, bathing suits laundered in phosphate-based detergents and sunscreen on swimmers.” Over the past few years, when Pollack was confronted with a malfunctioning salt chlorine generator, the manufacturer’s first question was always, “What are the phosphate levels?” As a result, Pollack recently decided to start monitoring and treating phosphates in all of her customers’ pools, as a matter of protocol. “We are treating our pools with phosphate remover,” she says. “I cannot yet say if it is helping the performance of salt chlorine generators, but I can say conclusively that it has improved our customers’ water clarity.” Pollack, enjoys the science behind water chemistry and plans to look at all the data they are collecting on phosphate levels at the end of the season. “It will be interesting to see if our documented data shows whether or not low phosphates correlate to improved functionality of the salt chlorine generators.”

SIX EASY WAYS TO CONTROL PHOSPHATE

[4] In a pool with a salt chlorine generator, it is important to be diligent about keeping phosphate levels down. The following are some guidelines that can help. • Test water for phosphates on a weekly basis; • Treat the pool weekly with a phosphate remover; • Use only non-phosphate metal products and cleaners; • Clean and remove grass, leaves and any organic debris from the pool as quickly as possible; • Test tap water (i.e. source water) to determine phosphate levels; and • Test for and treat phosphates after any periods of extreme weather or heavy swimming.

 

Terry Arko has more than 30 years experience in the swimming pool and spa industry, working in service, repair, retail sales, chemical manufacturing, customer service, sales and product development. He is also a Certified Pool Operator (CPO) and CPO Instructor through the National Swimming Pool Foundation (NSPF). Arko is currently the product specialist and northwest territory sales representative for SeaKlear Pool and Spa Products based in Bothell, Wash. He can be reached via e-mail at tarko@seaklear.com[5].

 

Source URL: https://www.poolspamarketing.com/trade/salt-chlorine-generators/

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