poolnerd

Since the last post on ozone and its use in pools, there have been a lot of questions and comments about salt water chlorine generators. Seems that alternatives to the old-school way of checking and adding chemicals is a hot topic. So, perhaps it’s time to take a closer look at salt systems. How they work, the sales pitch accompanying them, the perception, the reality. Examine plusses and minuses, let the informed consumer decide for him/herself.

Your Very Own Little Chlorine Factory

Here’s the quick story about how a salt water chlorine generator works. First, you dump a whole bunch of salt (regular old table salt or sodium chloride, NaCl) in the pool. It splits into sodium and chloride ions. Those chloride guys will be used to make hypochlorous acid (HOCl), the killing form of chlorine. And, by the way, whether you dump in liquid or granular chlorine, a little bag of shock, use tablets, or even inject chlorine gas into the pool water, the end product is the same: either hypochlorous acid (good) or hypochlorite ion (not so good), depending on the pH of the pool water.

Anyway, back to how the salt cell works. We’ve got sodium and chlorine ions from the salt we’ve added to the pool. This salty water flows over charged plates inside the the salt cell, and the electricity at those plates cause some magical chemical reactions to take place. It gets kind of technical and geekish, but here’s the basics of what happens, in chemical equations:

In other words, salt + water (plus a bit of electricity magic) gets us hypochlorous acid + sodium hydroxide + hydrogen gas. Incidentally, these facts are taken straight off a prominent manufacturer’s web site. If you look closely, you’ll see that the H’s, O’s, Na’s and stuff don’t balance on both sides of their equation; the equation above is more accurate.

Let’s look closely here, though. It’s important. The left side of the equation is pretty clear: salt plus water. Check. Now, the right side. Hypochlorous acid, which we’ve already talked about, is the most important part of what’s going on here, the “chlorine” part of chlorine generator. Next up is sodium hydroxide, more commonly known as lye, or caustic soda. It’s a very strong base, which, you may remember from basic chemistry, is the opposite of an acid. You’ve probably even got some sodium hydroxide there at your house — they use it in drain cleaners. And hydrogen gas, well, we all know what that is, right?

Those last two, sodium hydroxide and hydrogen, have some implications that we’ll return to later. But for now, let’s move onto the sales pitch.

The Sales Pitch

If you’ve ever talked to someone who sells these salt water systems, they’ll tell you that they’re the wave of the future. “A friendlier form of chlorine,” or “You won’t need to test your water any more,” or “No need to store or transport chemicals,” and a bunch of other stuff.

Keep in mind these folks are sales people. They’ll tell you anything to get you to lay your bucks down.

Now don’t get me wrong, salt cell systems aren’t the root of all evil or anything, I just happen to think they’re way oversold. They can’t possibly live up to all the hype.

So let’s get down to brass tacks, so to speak. The reason most people are interested in a salt water chlorinator is to save time and/or money. After all, who wants to test the pool water every week when this wonderful device will take care of everything for you? And need it be asked who wants to buy chlorine when it can be made for free right at your pool?

But the honest truth is that you’ll still need to test your water on a regular basis. The chlorine level output of the generator will need to be adjusted as the swimming season progresses: chlorine is broken down by things such as sunlight, heat and bather load. In March, you’ll need a lot less chlorine than you do in August. And just as critical as the amount of chlorine is the pH of the water. If it’s too high or too low, it can cause eye irritation, affect the plaster, cause scale formation on the pool tile, and many other factors. Believe me, you need to monitor pH closely and adjust as required.

Remember when I told you that we’d return later to sodium hydroxide, one of the byproducts of chlorine generation? Well, here it is. Since the chlorine generator is making a strong base, sodium hydroxide, as it makes the hypochlorous acid (the killing form of chlorine that we want, which is very weak as acids go), the pH of the pool water rises: really strong base plus weak acid equals, after varying pH’s kind of neutralize, a sort of strong-to-middling base. So, as chlorine is made, the pH goes up, too. Which in turn means that you need to add acid regularly to counter the pH influence of the sodium hydroxide. If you don’t, you’re in for red-eye and other types of swimmer discomfort, possible plaster degradation, rapid accumulation of scale on your tile, and other nasty stuff.

That doesn’t sound too hot, huh? So much for “easy.” But what about saving you money?

Well, it does … sort of.

Obviously, you won’t need to buy chlorine. But we all know that nothing is free, so let’s look a little closer. Ignoring the upfront cost of the unit, let’s look at just the upkeep costs for now. Every three to five years, the guts of the generator, the electrical cell portion, will need to be replaced. That runs about $600 currently. If you break that down into per-year-cost, that’s pretty close to what you’d spend on regular chlorine, like the plain old liquid stuff they sell at the local pool store, for example. Either way, using a chlorine generator or dumping dumping chlorine in the pool, you’ll be laying out about $150 or so every year to chlorinate your pool.

So, in a nutshell, a chlorine generator won’t really save you either time or money.

You will still need to test your water regularly, adjust the chlorine output on the generator unit as the season and usage patterns change, and monitor your pH closely. And you need to plan on spending some money, one way or another, to keep chlorine in your pool.

Heck, we could go through all of the sales blurbs one by one, but there’s only one real compelling point about salt water chlorine generators that I cannot dispute. The feel of the water. Softer, silkier. It’s pretty much the same thing as soft water, from what I understand. Lots of people love that quality. I can’t argue with something subjective like that, I can only lay out the objective facts without the accompanying sales hype, and let the informed consumer decide.

But let’s get back to our journey through the jungles of the salt water chlorinator.

The Nature of Salt

Another thing not mentioned in the sales pitch is that salt, by its very nature, is corrosive. In areas where they put a lot of salt on the icy winter roads, or in cities near the ocean, any of the local inhabitants can tell you about the effects of salt on metal components. Rusted-through panels on cars. Corroded metal railings. Spalled concrete. The list goes on.

This can happen to your pool, too. I’ve seen it.

I’ve got a pool I built that I put a salt system on about three years ago, for instance. There’s a column base, one of those galvanized steel patio cover post brackets, about four or five feet from the water’s edge. Well, I was out there to check a problem with the pump a few months back, and I was shocked at the amount of rust and corrosion on that thing. No doubt, some of the structural value of this underpinning has been compromised, but I was also surprised at the amount of staining — rust — on the surrounding deck area. Now, I’ve got dozens of other clients with similar installations except for the salt water, and they all seem to be fine. No staining, no corrosion, no problems reported or observed.

I’ve heard stories, too, of other pool builders’ projects where coping and waterfeatures were degraded by what they believe was salt corrosion. I can’t honestly say that I’ve seen that myself however. But, you know, all this stuff together, well, it kind of makes you wonder.

Besides being corrosive, salt is bad for many types of landscaping. If you think picking out plants that are OK with chlorine is difficult, try selecting ones that are salt tolerant, too. Talk about a nightmare! Furthermore, some municipalities don’t allow salt water pools, period. They have concerns about the environmental impact of salt on the soil and vegetation.

Anyway, it comes back to the nature of salt itself. Whether you believe the salesman’s pitch or not, salt has some fundamental properties that simply can’t be disputed.

Safety

One other thing that I said we’d return to later: hydrogen gas, another byproduct of the chlorine generation process. Hydrogen gas, when combined with an oxidizer, like the oxygen in the air, can be violently explosive. The infamous Hindenberg disaster demonstrated that vividly. But where would the oxygen inside a pipe filled with pool water come from? Evidently, above certain voltages at the cell plates, part of what goes on besides the chlorine generation magic, is that water molecules are also split, generating oxygen. The chemistry and such gets a bit much for me to grasp, but some pretty intelligent people have asserted that this can, and does, occur. So, hydrogen and oxygen are combined together in a pipe at the pool equipment pad, just waiting for something, some source of ignition, to combine them explosively. A confluence of unusual factors need to come together for all this to happen (no water flowing, a faulty flow sensor allowing continued production of the necessary gases, a spark to start things off). It is freakishly rare, but it does occasionally happen.

I’ve even seen this happen to a pool here locally, one with salt water chlorine generator. Boom! — there were shards of PVC pipe over forty feet from the point of the explosion. This wasn’t just some unexplained buildup of pressure, this was more like a bomb going off in this guy’s backyard. Luckily, it happened in the middle of the night and no one was around. Can you imagine if kids had been playing nearby? Yikes …

All the factory engineers and stuff couldn’t explain how or why it happened, but after a bit of Googling, I started to learn more about this rare, but potentially deadly, aspect of salt systems. The manufacturers build in safety devices, of course, but every once in a great while, something weird will happen. I must emphasize that it is very rare, but I also must say I certainly don’t want it happening on one of my projects.

I’ve also heard of corrosion of bonding points and other stuff that impact the safety of a pool. A blog covers more of this kind of thing in detail, as well as other aspects of salt systems. This blogger is against salt water chlorinators, extremely so, but he does make some good points that somewhat counterbalance all of the hype out there.

Sure, I’d Make Some Money, But …

When I try to sum up my views on salt water chlorine generators, I guess that’s the main thing: too much hype. People are looking for something to simplify their lives (after all, who wants to mess around with pool chemistry and all that?). Salesmen know that and are eager to sell you the miracle unit that they promise will do just that, and more.

But, folks, let’s be blunt and honest: maintenance is a fact of life when you have a pool. Bottom line is that a salt water chlorine generator won’t save you time OR money. and there’s no escaping the nature of salt itself and the ravages it can inflict on your pool, your landscaping and other parts of your yard. The downside just seems too great to me.

Here’s what I tell prospective clients when they ask about salt chlorine systems. I explain the stuff that we explored above, delving into even more detail as they ask about certain aspects. Then I tell them my honest feelings. “I’d love to sell you one of these systems,” I say, “I’m not going to lie to you, I’d make a nice profit on it. But, to be honest, I can’t recommend one. In fact, if someone I knew was getting a pool built, I’d have to tell them, all things considered, it’s not worth it. Don’t go with a salt water chlorine generation system.”

This entry was posted on Thursday, March 29th, 2007 at 1:00 pm and is filed under Uncategorized, Constuction, For Homeowners, Water Chemistry. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.