Saturday, October 14, 2006


WHY SALT SUCKS




So, do I have your attention now? Yes, I know. Cheap trick. But I’m trying to be combative here. Trying to get the juices flowing. Trying to get some FEEDBACK.

By the way, that's a picture of two year old limestone. Pretty, huh? It used to be, before the salt ate it.

Oh, and if you[re just tuning in, click on the September archive and read "salt belongs in the shaker, not the pool" first.

Is there no one out there who wants to defend these salt systems? No?

Good. I win. Remove them from all the pools and stop selling Pool Salt. God sakes. Do you believe it? Bags labeled Pool Salt.

"Our NaCl is better than the NaCl they sell at Home Depot. Sure, it costs more. But it’s better! Don’t use anything but genuine Pool Salt!"

Have we no shame?

But then, we mark up baking soda 1,000% and call it Total Alkalinity Control, so I guess we don’t. Yes, I know. It’s the box they’re paying $18.99 for. Not the 12 lbs. of baking soda inside.

I did receive one comment from my first post. Baboosa put me on to a new term; Galvanic Corrosion. And, boy, is it a duesy.

"Galvanic corrosion, often misnamed ‘electrolysis,’ is one common form of corrosion in marine environments. It occurs when two (or more) dissimilar metals are brought into electrical contact under water. When a galvanic couple forms, one of the metals in the couple becomes the anode and corrodes faster than it would all by itself, while the other becomes the cathode and corrodes slower than it would alone. Either (or both) metal in the couple may or may not corrode by itself (themselves) in seawater. When contact with a dissimilar metal is made, however, the self-corrosion rates will change: corrosion of the anode will accelerate; corrosion of the cathode will decelerate or even stop."

http://www.ocean.udel.edu/seagrant/publications/corrosion.html

Just so you know, most salt cell plates- or maybe all, I’m not sure - are made of titanium. Titanium is near the top of the chart for Cathodic metals. The cathode is the one that won’t corrode when galvanic corrosion takes place. So your salt cells are safe.

But it’s a good news / bad news kind of thing.

Copper, stainless steel and brass - or heat exchangers, filter tanks and water features, as I like to call them - are all pretty much anodic metals in relation to titanium. Remember now, the anode is the one that corrodes faster than it would if there weren’t any cathodic metals around.

You need three things for galvanic corrosion to occur. They are:

1. Dissimilar metals. We have that. Titanium salt cell plates and copper heat exchangers, for example. Or, titanium salt cell plates and stainless steel filter tanks, as another example. Or, titanium salt cell plates and brass pencil jets, or cannon jets, or high dollar sheer descents, to name a few. Brass is interesting in this scenario. It is made of zinc and copper. Copper is in about the middle of the galvanic index of metals. But zinc is all the way at the negative end, making it very susceptible to galvanic corrosion. That makes brass kind of ripe for this to happen. There’s something interesting about the titanium, too. It was chosen by the manufacturer because of it’s corrosion resistance (I read that in their sales brochure), because of it’s cathodic properties. Now, let’s add voltage to it. Does that make it more cathodic and speed up the whole process of galvanic corrosion for the anodic metals? Any science guys out there want to comment on that?

2. Electrical contact between the dissimilar conducting materials. It can be direct contact or a secondary connection such as a common grounding path. You know, like water as a grounding path.

3. Electrolyte (the corrosive medium) in contact with the dissimilar conducting materials. You know, like salt water.

Number three ought to keep any of you who thought you had me with, "then why haven’t stainless steel and copper galvanically corroded each other before salt systems came along?"

They would have. They were just waiting for the electrolyte to show up.

"Water is a compound that has strong ‘bonds’ among its constituents. In other words, it is difficult to break apart the hydrogen and oxygen atoms without some sort of energy input. ‘Salts,’ on the other hand, usually have weak ‘bonds’ and the atoms of salts can easily be separated into its appropriate ions. When a salt, like sodium chloride (table salt) is dissolved in water the sodium and chloride separate temporarily. The sodium atom will become a positively charged ion and the chloride atom will become a negatively charged ion. An ion is an atom or group of atoms that has a negative or positive electric charge. Negative ions are formed by atoms gaining electrons, and positive ions are formed by atoms losing electrons. Substances that conduct electric current are called electrolytes. They are formed as a result of a dissociation into positively and negatively charged particles called ions, which migrate toward and ordinarily are discharged at the negative and positive terminals of an electric circuit, respectively. The most familiar electrolytes are acids, bases, and salts, which ionize when dissolved in such solvents as water. Many salts, such as sodium chloride, behave as electrolytes when dissolved in water. Pure water will not behave as an electrolyte."

http://msnucleus.org/membership/html/k-6/wc/oceans/4/wcoc4_2a.html

Now, we should have known that. All of us. We should have known that the first time we poured salt into a pool we were creating a 20,000 gallon electrolyte battery.

You should have known it. I should have known it. We all should have known it.

Because if you cut and paste the link into your browser, you’ll see that the text description of electrolyte is from a fourth grade science experiment designed to teach ten year olds "that the ions in the water make salt water an electrolyte. An electrolyte is a nonmetallic electric conductor in which a current is carried by the movement of ions". In the experiment, the children observe that as they begin to add salt to the water, the water begins to conduct electricity, and the light begins to glow. The more salt they add, the more brightly the light glows.

Now that we’re all properly embarrassed, go back to the last sentence in the description of an electrolyte: Pure water will not behave as an electrolyte. Granted, our pool water is far from pure, but the old NSPI guideline limits TDS to 3000 ppm. Tap water ranges from 250 to 600 ppm. The highest I ever saw was 465 ppm out of the tap in El Cajon, CA. But I’m sure there’s harder water than that out there. The point being, we used to drain pools when they started approaching 3,000 ppm TDS. That’s where we start talking with salt systems.

Hence this discussion about galvanic corrosion. It was never an issue before. Now it is.

For example: Everybody knows by now, even those who defend salt systems, that you ought not to install a stainless steel DE filter tank where you have a salt system. I believe that more than half the reason is galvanic corrosion. I think another part is a little known issue called chloride stress corrosion, a problem unique to stainless steel, pressure, high water temp and brine, but we’ll talk about that at another time. Back when this whole salt craze started, I had a brand new pool on service that had a salt system and a stainless steel filter tank. The tank had pinhole leaks within ten months. Another one, a painted stainless steel tank (betcha can't guesswhich one) lasted a full year before it started weeping at the welds.

On the other hand, I have pools on service that are so old that a few still have American Products Titan stainless steel DE filters, but no salt system. Twenty years later, the tanks are just fine.

When you rule out stainless steel filter tanks, you automatically rule out 72 square foot DE filters and give up 12 square feet of filtration area. Because the largest non-corrosive DE filter tank is 60 square feet.

Now, if you’re a good and conscientious builder, you know that anything larger than a 2 horsepower pump will eventually crush those grids, and in some installations, even just 2HP is going to cause premature deterioration of the grid pack.

But your customer is adamant about having a salt system - because his best buddy does and the water feels so totally cool - and at the same time he really wants those spa jets to sing and dance, and you’re trying to squeeze in all the water features that he wants on that single filter pump and still keep your bid right so that you don’t lose the work to the competition who doesn’t care about pump and filter sizing.

Of course, if you take salt out of that equation, the problem goes away.

Further, I believe that the recent attempt to introduce cartridge DE filters - where you can get up to 100 square feet of DE filter area in a plastic tank - has been driven by the problem of salt and stainless steel.

Talk around the campfire is that we are probably in for a bit of a wait before they get the kinks worked out of cartridge DE filters.

Once again, though, the way we’re finding out that there’s a problem is by buying them, selling them, installing them and then spending all of our profit on complaint and problem calls, not to mention being totally defenseless when the customer asks, "didn’t you check this thing out at all before you sold it to me?"

But the salesman said...

At least with something like a filter problem, the worst case scenario is installing a different filter and a little bit of vacuuming to suck up the DE that blew into the pool when the cartridges crushed.

With salt, and a litigious consumer, you’re looking at the possibility of being on the hook for failed filter tanks, crushed grid packs, salt damaged coping and decks, failed copper heat exchangers, deteriorating brass water features that put metals into the pool water that will eventually plate out, and subsequent acid washes or replastering. High concentrations of salt will also kill trees and most any other type of vegetation and erode the soil (see my first post: salt belongs in the shaker, not in the pool). If you’re the one that installed the sticky water leveler and the salt system, are you liable for the damages?

Or maybe we should just sell them where they’re appropriate. You know, like for a pool that uses no concrete (salt water freeze/thaw issues), or stone (deterioration issues), or metal (galvanic corrosion issues), or is surrounded by soil, or plants or trees (environmental issues), or backwashes to the sewer (waste treatment salinity issues), or backwashes to the street (once again, environmental issues), or ever has to be drained to the sewer or the street (the same waste treatment and environmental issues).

We can, of course, just keep selling salt systems, and when things go south, keep walking away. That seems to be most folks answer. Because the truth is most customers don’t litigate. They just say bad things about us until they die. But it seems like these kinds of things just keep happening over and over and over again in our industry. Things like that first generation salt system that used to blow up if you left it unattended for too long, or the ionizers that turned pools copper green and purple, or pencil thin filter tank clamps that aged and blew the lids off and into people’s faces, or single source drains in spas, or... do I need to go on?

Maybe that’s why most homeowners and the other trades look at us like the Corky’s of the construction and service industries.

Maybe if we stop letting greed and avarice cloud our minds, and maybe if we stop looking to the manufacturers for pat answers instead of fixes, and maybe if instead we ask more hard questions up front before we buy to resell...

Yeah, right. And maybe bats will fly out of my butt.

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Comments:
I guess people don't put sealer on Limestone coping to protect it like they used to. It is a very soft material afterall and heck, a little acid rain can eat it away. Can you explain how the salt makes the water acidic enough to accelerate the erosion process.
 
First, I just want to respond by saying that you or I can't control whether acid rain falls on our customer's pools. We can, however, help in making the decision whether they ought to have a salt system. And, "go ahead and get one. Acid rain's gonna screw up your limestone anyway," doesn't strike me as a good reason to say, "Aw, why not sell 'em salt, too."

I don't think that in the case of salt pools and limestone, it's even acidity that's causing the erosion. I think a part of the problem can be chalked up to what these guys:

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6W6G-46MC6NV-8&_coverDate=09%2F30%2F2002&_alid=463204831&_rdoc=1&_fmt=&_orig=search&_qd=1&_cdi=6598&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=4e06656a402303c85c8bd33fa4463c9d

are talking about when they discuss how the simple passage of liquid heavy with chloride through some types of limestone causes damage. Their conclusions point to the crystalization of the chloride inside the stone once the water that brought it into the stone evaporates, and how that crystalization causes the damage.

Then, these guys:

http://www.ingentaconnect.com/search/article?title=Salt+damage&title_type=tka&year_from=1998&year_to=2006&database=1&pageSize=20&index=17

who talk about how the freeze/thaw characteristics of water change when you add salt to the water. Their study dealt with concrete, and how salty water reduced the mechanical integrity of the concrete as the water freezes and thaws, causing cracks in the concrete.

Then there's just the plain old fact that salt is corrosive. Take two pieces of metal. Put one in a bucket of water, the other in a bucket of salt water. Which one corrodes faster? Why should stone, especially a soft stone like limestone, be any less effected?
 
For galvanic corrosion to occur there have to be TWO separate paths for the electrons to flow. You mention one of the paths which is the electrolyte which passes ions through the liquid (ions carrying charges, of course). However, the other path is electrical where the metals pass electrons between each other. In an electrolytic cell, this is done through wires, but in your galvanic example with two dissimilar metals, this must be done by some direct contact or a wire attachment or some other method of electron transfer. Simply having two dissimilar metals in water that are not touching each other will not have one corrode faster than the other. They must be electrically connected.

You may recall that pipes are sometimes "protected" by having another metal that corrodes more readily put near them, but they are also connected electrically (via a wire) and if this connection is broken, the protection is gone!
 
Dear Chem Geek,
You are my hero. And you're right. Everything I go back and look at points to the validity of what you're saying. I wonder, though, could the fact that the cathodic metal in this case, ruthenium coated titanium plates, having a voltage applied to them for the electrolysis to occur, substitute as the wire you're talking about? In normal galvanic corrosion, two dissimilar metals create a difference of voltage potential just by being dissimilar, and the current flow takes place, robbing electrons from one and feeding it to the other. Could the added voltage applied to the cathode create the conditions we need? You have realy peaked my curiosity here and I'm going to talk to my metallurgist after the holidays and get his feedback on this. Because something is eating up filter tanks, ladders, handrails, heat exchangers, etc., and the manufacturers, while they won't say it's galvanic corrosion, do say that if you put a zinc ball in your pump basket, it'll fix the problem. Zinc's a sacrificial anode for...wait for it... Galvanic Corrosion.

Great, great comments! Please stick around and bitch slap me when I'm wrong!
 
Dear Chem Geek,

I'm going to do some more thinking about it, but I think I found that wire you were looking for. We call it the bonding wire. That explains eveerything except the filter tanks. Further, the more I hear you and Dynamictiger talking about stray currents, the more convinced I am that, even if it doesn't fit the textbook example of Galvanic Corrosion, that's what it is. But then, I'm "just a pool cleanup guy". I don't have the advantage of the view from the Ivory Tower. Just down here on the ground, where everything's turning to rust.
 
The bonding wire connects most metal surfaces that are in contact with water including pool pumps, ladders, lighting fixtures and any metal plumbing in order to ensure that no voltage difference occurs between them. Technically, since the metal pump housing is connected to the ground, this process essentially grounds all metal surfaces, but the purpose wasn't for grounding but to prevent voltage differences.

The titanium or other metal anode and cathode (these reverse in polarity every so often) will NOT be connected to this bonding wire. To do so would connect them to each other causing them to short and not able to produce the potential difference that is the basis for the electrolysis that generates the chlorine. These plates are exempt, so to speak, from the bonding requirement and their voltages are low anyway so should not normally cause a "shocking" problem.

At this point, it still seems like stray currents (or possibly free radicals) coming from the SWG may be the issue. If an SWG were installed downstream from a heater with a copper heat exchanger and if such heaters did not experience corrosion, then that would seem to be a simple solution to this problem.
 
As for putting a zinc ball in your pump basket, that will not work to prevent corrosion of other metals (e.g. copper in a heat exchanger) unless it is electrically connected to it (and the pump basket is typically not metal so not bonded to the heater). Just because a manufacturer says something, doesn't mean it is correct. You have to talk to technically competent personnel, not just sales people.
 
One possibility where the bonding wire might have an effect, though an indirect one, is to create an electrical circuit path that straddles the salt cell. The pump may be on one side and the heater on the other (though I'm not sure the copper heat exchanger is connected to the bonding wire -- I suspect it is not). That could cause stray current electrolysis where the stray current flows down (through the salt water) from the salt cell to the heater and then the bonding wire returns this current back to the upstream pump source. This sounds like a bit of a stretch as longer distance paths in the electrolyte mean more resistence, but the rapid flow rates might offset some of that.

The reason it is important to understand the WHY of what is going on is so that a solution can be found. Simply saying "don't use salt cells" is too simplistic as they do provide many benefits. I hope this problem does get solved.
 
One possibility where the bonding wire might have an effect, though an indirect one, is to create an electrical circuit path that straddles the salt cell. The pump may be on one side and the heater on the other (though I'm not sure the copper heat exchanger is connected to the bonding wire -- I suspect it is not). That could cause stray current electrolysis where the stray current flows down (through the salt water) from the salt cell to the heater and then the bonding wire returns this current back to the upstream pump source. This sounds like a bit of a stretch as longer distance paths in the electrolyte mean more resistence, but the rapid flow rates might offset some of that.

The reason it is important to understand the WHY of what is going on is so that a solution can be found. Simply saying "don't use salt cells" is too simplistic as they do provide many benefits. I hope this problem does get solved.
 
Dear Chem Geek,
It seems that the more you explain, the closer you come to saying galvanic corrosion. Not to put words in your mouth, but it starts to sound that way. Further, a properly installed salt system control unit is grounded to the same bonding wire as the heater, the lights, the ladder, the pumps, etc. The cell is electrically connected to this grounded electronic unit. I understand impedence and isolating it thus, but it is still part of the loop. So is the heat exchanger in that the heater is on the bond wire, metal to metal all the way from the bonding lug to the heat exchanger. You talk too about just placing the salt cell downstream from the heater and all the problems go away. All salt systems I've ever seen are installed downstream of the heater output. Yet the problem persists. It persists so strongly that heater manufacturers are scrambling to come up with cupro nickel headers for salt applications. And we still haven't figured out why unbonded stainless steel filter tanks that'll last twenty years in a standard pool won't last 18 months on a salt pool, when the closest any manufacturer will come to stating the level of salt at which corrosion occurs is Pentair, who state in their FAQ's that corrosion of metal parts may occur at levels above 4,000 ppm. You misunderstood about the zinc balls, too. That wasn't from a sales rep. That was from a technical instructor at a Pentair training seminar on 10/17/06. Graduates of that training seminar were considered qualified to register as Pentair warranty centers. So, the problem isn't just uninformed sales reps. It's an uninformed industry. I just stumbled onto you guys by posting at what I thought was a consumer forum about pools. Which reminds me to ask; who are you? Where are you? What is your position in the industry? Why aren't there tons of articles in Pool & Spa News and Aqua magazine about your theories on stray currents and such? I'm not doubting you at all. I'm just wondering how you know so much and seem to be so close to the industry, but the industry is so clueless of your findings. About your conclusion that we need to resolve this so we can keep selling salt, I have to strongly disagree. I'm of the opinion that we need to suspend sales and resolve these issues. Then, once they're taken care of, then and only then, start selling salt again. But to keep selling it in light of all the problems, especially if we can agree that the problems are occuring, is not responsible or good corporate citizenship.
 
I am not associated with the pool industry at all. I am just a pool owner with a strong chemistry/physics background and an interest in pool water chemistry. I am NOT an expert in corrsion.

The bonding wire that you say is connected to the SWG is simply connected to the same box that also has power connected to it and has wires coming out from it to the salt cell. That does NOT mean that the wires from the salt cell are connected to the bonding wire. If they were, then the salt cell would not work (because the two plates would be electrically connected to each other instead of connected to two sides of a transformer with a potential difference). The "hot" side of 120V electrical power is obviously not connected to the bonding wire so you shouldn't assume that all wires leading to a box are possibly connected to each other.

As for the salt cell being downstream, the only reason I assumed it was upstream were the comments people were making about high chlorine content being a culprit. Chlorine generated from the salt cell won't flow "upstream" so that's why I assumed the SWG came before the heater in the flow. If it doesn't, then that eliminates some possibilities.

There are some people who add salt to their non-SWG pool "for the feel of it". Do they also experience corrosion with copper heaters not explained by things such as high acidity if someone puts a Trichlor puck in a skimmer basket without the pump always running?

If the bonding wire is contributing to the stray currents by completing the electrical path, then it should be trivial for someone to simply insert a current meter at the bonding wire to the SWG or to the heater or both and simply measure if there are currents and in fact can calculate the amount of possible corrosion based on the amount of such currents (if present).

There are many, many users with SWG and others with salt added to their pools that have not experienced any problems with either corrosion of heaters nor of pitting or problems with their decking, so it would be irresponsible to just halt sales of SWG or of adding salt to pools. There are also issues of the industry not disclosing the problems of high CYA, but that doesn't mean it shouldn't be used since using a smaller amount of it is good.
 
Dear Chem Geek,

I see your point about the transformer. But at the same time, will that transformer work without a ground? No. It won't. Does that mean that the applied voltage is shorted to that ground? No. It isn't.

I've read in the Garden Web forum about people adding salt to their pool just for the feel of it. I wonder the same thing about whether, in the long term, they will experience any problems that I currently attribute to galvanic corrosion, seeing as how they don't have the salt cell installed and turned on. You see, I think it has something to do with the fact that the titanium plates are so far up the cathodic side of the galvanic index, while the metals being damaged are at the other end of the index, or at best, several steps down the list from titanium. These conditions,whatever they are, may not fit the classic definition of galvanic corrosion, like a salt cell battery does, but it is very galvanic-like, and it is very real, and I believe that if you remove the power from the cell and the salt from the water, you remove the incidence of corrosion.

As far as comparing what's going on to people putting 3" tabs in their skimmmers, even us "pool cleanup guys" know that only an utter dolt uses his $2,000 plastic skimmer in place of a $10 plastic floating chlorinator, or a $90 tab feeder. And those of us who work with pools are taught that about week two on the list of "oh, by the way, don't do these things. #1. Never put tabs in the skimmer basket. It acid washes the heater every time you turn the pump on". If you have a poolman who does that, and he's not doing it for a couple of days only, with the pump running twenty four hours a day, for some major swamp cleanup kind of thing, fire him. Without discussion. Fire him.

Off the subject, I once did a little test with Bio Guard skimmer sticks, that are only supposed to dissolve with erosion. I tested the water in the skimmer every day for a week, right before the pump turmed on for it's daily run, after the pucks had been laying in there all night long. Every morning, my pH reading was piss yellow.

So much for Smart Sticks.

You say there are many people who have salt systems and have never experienced any problems with their stone work, decks or any metal corrosion.

What I say to that is: Not yet. You know, John Wayne used to advertise for Camel cigarettes. Thirty years later, he died of lung cancer.

Everybody loves salt. Until someone like me walks in their back yard and points out that the flaking on their hard stone coping that they thought was normal isn't normal. Or the spawling in their limestone or travertine is happening about ten or fifteen years ahead of non salt pools. Or the reason their pool is always dusty is because their snadstone coping is slwowly dissolving into their pool. Or I ask them how many times they've replaced the Drive Shaft Assembly on their Polaris 280 and they learn that once every year or two is a lot, and that non salt pools do it about once every never. Or I point out that the rust around their diving board stand isn't normal for other pools. Or I point that the leaf burn in their flower beds isn't because of too much Miracle Grow, but from salt splash out. Or, about 6 months after the 1 year warranty expires, I repair their heater by replacing their calcified Teledyne Laars pressure switch, probably the single most reliable, long lasting part in the history of pool heaters before salt arrived. Or I explain to them that their Pentair heater is going to keep eating temperature sensors as long as they have salt water in their pool. Or I explain that the rusting on their pool ladders and hand rails above the water line is because of salt splash and the only way to stop it from occuring is to get a towel and completely wipe dry the ladder and hand rail after each use. Ot I ask them if they put all the money they saved by not buybing tabs in a piggy bank, because it's time to crack that baby open and buy a new salt cell.

Then I ask them if they think that their soft skin and tangle free hair is really worth all these side issues. Even your own Pool Forum talks about the addition of sodium tetraborate to get the silky soft, sparkly water.

Before salt, filter tanks had a ten year warranty. Now it's one year.

You can't use anything larger than a 60 square foot DE filter with a salt pool/spa, which limits how big a pump you can to put on your pool/spa without crushing the grid pack in about two years. We used to be able to go as big as 72 square feet. But that's only available in stainless steel. Not compatible with salt.

Why do we need to keep turning our industry inside out to increase corporate coffers? Because all we're doing is turning our customers into lemmings rushing toward the cliff, all the time saying to each other, "isn't this great?"

No, it isn't. It's insanity.

So tell me. In all seriousness. What are the benefits of salt? And not the sales brochure "get rid of green hair" benefits. The real, scientific benefits. What are they?
 
Dear Chem Geek,

Could you e-mail me? Get my e-mail by clicking on the blue The Pool Guy icon at the top of any of my comments here. I'm hoping that we can also correspond that way because I'd love to get my hands on some of your references. Like this one you posted in Garden Web; "Now it is true that inside the salt cell in between the plates the chlorine level is quite high -- some SWG manufacturers have measured it at 80 ppm or so..."

I'd love to have the reference to that sort of source material, if you would be willing to share it.
 
I found out some more info on the use of zinc to inhibit corrosion. If the "zinc ball" was metal, then what I said earlier was correct, but if the zinc is oxidized into zinc ion, then this can inhibit corrosion. Typically the zinc (usually as zinc chloride) is combined with phosphoric acid and this combination is used to inhibit corrosion, but in a pool one does not normally want to add phosphates since that is a needed nutrient for algae.
 
P.S. (you can add this to my previous comment). The zinc forms a zinc oxide (in the presence of dissolved oxygen) protective layer on the metal.
 
Chem Geek,
I addressed the issue of the zinc balls you're talking aobut in the next installment of this blog, titled Res Ipsa Loquitur. Here is an exceprt about why you ought not to want zinc chloride in your pump pot.

...zinc chloride has a pH of anywhere from 1.8 to 4.0, depending on which Material Safety Data Sheet (MSDS) you look up. Here’s a couple I found online:

http://www.zaclon.com/pdf/zinc_chloride_granular_msds.pdf (This one says 1.8, )

http://physchem.ox.ac.uk/MSDS/ZI/zinc_chloride.html (This one says 4.0)

So, it’s either 1000 times more acidic than pool water, or 100,000 times more acidic, depending on which MSDS you believe. Tri-chlor tabs are 2.8 pH, or about 10,000 times more acidic than pool water, to give you a point of reference.

Neither of those numbers would be anything I’d want growing in my pump pots, though. It would be like putting tri-chlor tabs in the pump pot. Growing is what the zinc chloride does, by the way. As near as I can understand it, the zinc combines with the chloride and forms - you guessed it - zinc chloride crystals."
 
Damn you, pool guy. My AutoClear SWG has been failing and in my search for info on how best to repair it, I found your blog.

Looks like the best repair is to throw it out and start with something else. I am not comfortable with spending the $800 they want for a replacement cell.
 
CR, I feel your pain. That Auto Clear is a particularly unpopular model. And $800 for a new cell is highway robbery. Another thing about your salt system I bet they forgot to mention, huh?

There's an online article at Pool & Spa News right now about how to sell these Trojan Horses and they say that the dealers need to stress the payback on a $2,000 system by pointing out that you'll save $300 a year on chlorine, so the payback is 6 or 8 years. Except they don't mention in that equation that every three years you get to pop $800 for a new cell. So, now, at $300 a year "savings" on chlorine, your payback is $100 a year. Then, after you subtract the electrical cost of running the salt system, it's a wash.

But you do get to keep all the corrosion damage done to your pool. That's on the house.
 
Hi Chem geek and pool guy,
Found this blog and boy u guys are onto something. I too am battling this question on corrosion. here is my story. I have a hot tub with a swg eco spa generator. Made it one year and the inline heater started to show signs of corrosion around the heater terminal. It was replaced and my pool guy placed a zinc anode disc in the strainer basket and ran a copper wire to the bonding/ground terminal on the side of the balboa heater box. In 3 months the heater was toast. The stainless turned into a rusty dripy mess. The thought was that the swg was putting out too much clorine and maybe aggressive water since he had installed lots of these swg's without very many problems in our area. I questioned the bonding that was done from Coleman since it wasn't a contiuous wire linking all the pumps and heater together. So that heater was replaced and all the bonding was tightened down the way Coleman had installed it since most connections were very loose and dielectric grease placed on those connections. 2 months later now the new heater is destroyed....eaten up. He doesn't know what to think but I know it is stray current in salt water and dissimiar metals causing this. I also think, from my research, that the titanium plates and the stainless in the heater are reacting. The zinc anode goes uneffected since its not bonded to anything, at least thats my thought. One person in the industry suggested to bond everything together but don't hook that bond up to ground or back to the house panel as this is where you get stray current. This way everything is at the same potential. Also hook the zinc anode to the bond wire which it will complete that circuit and the zinc should dissolve and not the stainless heater. Thoughts?
 
PFLOVING: Check this out. You're comment warranted it's own blog piece, so you'll find my answer here:

http://thepoolbiz.blogspot.com/
 
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