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."
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."
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.