SWG How It Works

How Does a Salt Water Chlorine Generator create Chlorine in a Pool?

The SWG cell consist of titanium metal plates coated with a layer of mixed metal oxide catalyst (ruthenium monoxide and iridium). An electrical current of 18-36 volts DC is passed between the plates. The electronic control circuitry control the voltage and amperage in the cell.

SWG Price Changes

The coverage of the titanium plates is about 80/20 ruthenium/iridium oxide. When the price of the ruthenium part increases 400% it's obvious that prices for the entire cell has to increase. The plates alone for a T-15 cell cost $200 in 2018 where as in 2017 they were only about $50-60. Then there is the housing, electronics, cord and all the other fixed expenses before companies even get to their marketing expenses and overhead.

Since there are only a couple of suppliers for coating plates there is no room for price negotiations. Suppliers of the cells will simply pass the costs on to customers.

As of February 1, 2021, the price of Ruthenium has gone up 20% in the past 15 days and the price of Iridium has gone up 200% in the past 60 days. You have to remember the price of Ru increased 200% in 2019-2020. Since the coating on salt cell plates is about 6:1 Ruthenium/Iridium this translates into MUCH higher prices for a salt cell in 2021.

Reason given for recent Ir price increase is supplies from mines in South Africa has essentially been shut off due to variant Covid strain originating there.

SWG Economic Analysis

SWGs are often sold as hands off, to people who never learned their systems or the chemistry, and those are the disasters you hear about.

To figure out your ROI, it's pretty simple. For 26k gallons, each gallon of 10% chlorine nets you 3.84 FC. Here is your FC cost for the gallon prices you will likely see this season.

• $5 gallon = $1.30 per FC
• $6 gallon = $1.56 per FC
• $7 gallon = $1.82 per FC

Narrow down your SWG choices and find it's production of chlorine per 24 hours in poolmath. A 10k hour lifespan unit equals 417 days of straight production. Multiply the daily production by 417 to get your total lifespan FC produced. (In perfect conditions).

Take the cost of the SWG, controller and install costs if applicable and divide that by the lifespan FC for your cost per FC.

So let's take a Pentair IC60 system going for $1600 today. It produces 9.2 FC a day in 26k gallons, or 3836 lifetime FC.

$1600 system = $0.42 per FC which is about 1/3 the cost of the cheapest gallon of bleach for sale right now. In theory, over its lifespan, the unit will be 3 times cheaper than LC for you.

Installation costs if you don't DIY will take away some savings. If installation doubles the cost to $3200, you'll still save some on the first unit, but the future units will be the big paybacks.

The $569 controller usually lasts 3 cells so the next two replacements only need the $1100 cell, basically covering your installation costs, and if you DIY'd it, the replacement units will really pay off

$1100 unit = $0.28 per FC.

In summary, many would pay 3X the liquid chlorine price for the convenience the SWG provides. That 'payback' is literally priceless. With a SWG you spend less time on FC monitoring/adjusting from June to mid November. That includes getting the kit out, going out to get a water sample, and putting the kit away. Your FC can stay at high target or above and the thought of algae never entering your mind. *And* it can save you 2 or 3 times what the LC would have cost, not including time and effort.

Chemistry behind a SWG

Salt is sodium(NA) and chloride(CL). The Na and Cl break apart as soon as salt dissolves in pool water.

The chloride ions lose an electron at the cell plate to form chlorine gas Cl2.

Electrolysis is the process of removing an electron from the chloride and putting an electron on the hydrogen ions that make contact with the opposite side of the cell plates.

So, basically, a chloride ion is on one side of the plate and a hydrogen ion is on the other side of the plate and an electron moves from the chloride ion through the plate and onto the hydrogen ion.

The electrolytic cell generates chlorine gas at the anode and hydrogen gas at the cathode. The chlorine gas rapidly dissolves into the water and hydrates to form a mixture of HOCl/OCl- that is pH dependent and the hydrogen gas bubbles out of the return (hydrogen is not soluble in water).

Does a SWG Create Bubbles?

A SWG cell makes chlorine gas and hydrogen gas. The chlorine gas dissolves pretty fast and you won't normally see any coming out of the returns. Hydrogen gas does not dissolve very well. The gas coming from returns is hydrogen.

The only time that you can see chlorine gas is when you have a clear cell and can see the chlorine gas and hydrogen gas being generated at the plates.

Does Running a SWG at 100% Effect Cell Life?

Chlorine generators for pools operate far from ideal conditions and so the more stress you put on the plates by running them at a 100% duty cycle, the worse off the catalytic coating is going to fare.

There are two main factors that affect the electrolysis of chlorine gas - current density distribution across the plate and cell AND mineralization of the plate surface. In a bipolar electrolysis cell, the current “crowds” mainly at the edges of the plate and at any “hot spots” on the surface. Current crowding is a problem in any electrolytic setup. What it typically does is causes the catalytic coating to degrade along edges first and anywhere there are hot spots. At these high current density areas you also get greater precipitation of minerals, mainly calcium, from pool water. The calcium mineralization is non-conductive for the most part so it also exacerbates the irregular current distribution.

To abate some of these problems, cells are designed with a three electrodes where the outer plates are often ground and the center plate is charged. The plates are also set into non-conductive dividers to help keep the current from flowing around the edges where the electric fields are the least uniform. One then does periodic current reversal to alternate which side of the plates are anodes and which are cathodes. This helps to more evenly distribute the inherent damage across all plates as well as reduces the amount of scale formed on any one side. The plate spacing and voltages used are set to minimize as much current variation as possible but there will always be current bulge due to a flowing electrolyte.

My admonition is this - the more you can let a cell “rest” by keeping the output % low, the more chance you give for mineralization to be redissolved into solution. The more you drive the plate with no OFF time, the more those plates sit in a high pH, highly oxidative solution. That chemistry can not only cause the precipitation of scale but also the dissolution of ruthenium metal from the plate. The Pourbaix diagrams for the stability of ruthenium species in chloride solutions gets very complex with multiple different soluble species being possible. Ruthenium is a weird metal in that some of its oxides are insoluble while other oxides can actually exist as a gas phase. Ruthenium hydroxides and chlorides are very soluble in water. It’s complex behavior is what gives rise to its usefulness as a catalyst.

I’m not saying an SWG owner can’t run a cell at 100% when it’s necessary. But it’s far better to design a system where that is unnecessary. You can certainly take the position that you should just drive it as hard as you can and hope for the best, but I guarantee that will not get you the published lifetimes on these cells. I don’t think there’s any way to a priori know how long a setup will last, but prudence is always the safest bet.

How to Clean a SWG Cell

You should only clean a SWG cell if it has visible scale on the plates.

Try and clean with the process that will do the least damage to the rare metal plates and then move to more aggressive methods if necessary.

Cleaning a SWG cell with Water

First try and use strong blasts of water to remove the scale. One member found success using a WaterPik.

Cleaning a SWG cell by Scraping Plates

You can scrape the plates with a stick, like a Popsicle stick, to remove the scale.

Cleaning a SWG cell with Vinegar Acetic Acid

If the scale is stubborn then use cleaning vinegar (6% acetic acid … available in Home Depot). It’s milder than Muriatic Acid and won’t damage the ruthenium surface. Highly concentrated mineral acids are not good for the transition metal catalysts.

Cleaning a SWG cell with Citric Acid

On a molar basis citric acid will be “stronger” than either acetic acid or ascorbic acid. So it will produce a solution with lower pH due to more acid protons (H+) being released. This is why your perception is that it works better on scale than vinegar does.

All acids will remove a small amount of material from the ruthenium surface because ruthenium oxide is not stable in acidic conditions. Ruthenium metal itself is highly reactive to air forming ruthenium oxide. In water, a pure ruthenium metal surface will slowly oxidize based on the amount of dissolved oxygen in the water as well as oxidation formed by hydrolysis. So, if you leave a chunk of ruthenium in highly acidic water for a long period of time, it will dissolve.

The key to cleaning calcium scale off the plates is to use an acid that is strong enough to destabilize the carbonate anion (force carbonate to become CO2) and remove the calcium without the acid also etching the ruthenium metal. The conjugate base of the acid matters as well. Chlorides and sulfates do increase the likelihood of reforming ruthenium oxides quickly enough at the ruthenium metal surface such that hydrochloric acid and sulfuric acid would be poor choices. Ascorbate ions from ascorbic acid tend to be anti-oxidants and will less likely increase the repassivation of the metal surface. Acetic acid creates acetate ions which also weakly interact with ruthenium. As far as citrate goes (the conjugate base of citric acid), I'm not entirely certain as I would have to search the literature for it. My guess is it will be more aggressive towards ruthenium than either ascorbic acid or acetic acid but much less aggressive than muriatic acid. Citrate tends to act as a chelating agents to many transitions metals like iron and cobalt so I would expect ruthenium to complex pretty readily with citrate given the many different stable oxidation states that a ruthenium atom can attain. Ascorbates and acetates are weaker chelating agents.

Vinegar can be just as effective but if you don't happen to have vinegar lying around, and the big bag of citric acid is just sitting there screaming to be used, then you can use it without much harm. There's no need to make highly concentrated solutions. A few % of citric acid in distilled water will effectively soften or remove calcium scale. Then just hit it with a garden hose spray to flush it out.

Cleaning a SWG cell with Muriatic Acid

Cleaning a SWG cell with Muriatic Acid 10:1 diluted solution will remove some of the rare earth coating from the plates and reduce the life of the cell with every cleaning.

History of SWG

Diamond Shamrock Corp. created the Lectranator in 1976. A patent was filed for on 11-11-1976 and granted on 7-11-1978 - DOCUMENT ID: US 4100052 A - APPLICATION NO: 05/740870. The patent description was:

Disclosed is an electrolytic cell for the generation of low cost halogen biocidally active agent from an aqueous solution having a low halogen salt content for use in the treatment of sewage or other liquid effluents, especially those of fresh water swimming pools or fresh water cooling towers.

The electrolytic cell is used in line with pumps generally associated with the distribution of waters for swimming pools or cooling towers.

The present invention generally relates to an electrolytic cell for the generation of low cost halogen biocidally active agent for the treatment of a sewage or other liquid effluents especially those waters of a fresh water swimming pool or cooling towers. More particularly, the present disclosure relates to an improved electrolytic cell having a bipolar configuration which is used in line with the pumps generally associated with the distribution of waters in swimming pools or cooling towers or other liquid effluents for the generation of chlorine from affluent containing low levels of chloride.

This employs an enclosure connected in line with the liquid distribution system of the facility containing a series of parallel planar plates to be utilized as electrodes arranged such that the effluent flows through the parallel planar matrix of plates and is treated thereby with the chlorine being electrolytically produced from within the confines of the electrolytic cell.

The Lectranator has been in production since 1978 (16 years before the AquaRite).

Lectranator Corp was sold to Olin and then to Team Horner in May 1992 and this became the AutoPilot SWG.

Goldline Controls®, began as Independent Energy, Inc., a company founded in 1975. In 1994, the company began producing Aqua Rite® salt chlorinators for swimming pools.

Hayward® Industries, Inc. acquired Goldline Controls® in August 2004.