Sunday, March 25, 2007

Stray Currents Are Still Dissolving Your Salt Water Swimming Pool, Part Three

I have tossed around the term Stray Current a lot lately. Before, I always thought of it as just another name for Galvanic Corrosion, until I was contacted by a pool builder who specializes in in-ground vinyl lined pools. He explained how he had been chasing Stray Current Corrosion issues for the last fifteen years, since way back to the Lectranator days. Once I started reading up on Stray Current Corrosion, about three weeks ago, I found that it's prevalent in DC systems. Like our salt systems. When you add in the Galvanic Mismatch of the metals we use in our pools, it explains a lot.

I’ve printed his comments about the problems he’s seen in previous blog pieces. In fact, his quotes are what started me titling my weekly installments as “ Stray Currents Are Dissolving Your Salt Water Swimming Pool”.

You see, it wasn’t until I talked to him that things started really gelling in my head and I was able o say that I really understand the theory what’s happening to our pools with salt water chlorination. That’s what the manufactures are counting on; that it’ll be too hard for us to put all the disparate pieces together to overcome their lies.

Like when I first started asking questions about why everything was falling apart, they would say, “We’re only using 3,000 ppm salt. How could that be corrosive? Salt’s not corrosive until…” then fill in the blank with the myriad BS salt levels they come up with.

Then, when I asked, “What about galvanic corrosion?” they said, “It can’t be galvanic corrosion because the metals aren’t touching.” And that answer really stumped me for awhile. I couldn’t figure out how to get around that. I knew the pool metals were corroding, and I knew that it was really only happening so very rapidly on salt pools, but the truth is the metals weren’t touching. So what was causing it?

Then I got his first e-mails, where he talked about chasing Stray Currents and talked about how those Stray Currents were corroding the lugs off the pool bonding wires, and everything started making sense.

So, I asked him for a procedure that we could all use to see for ourselves what was going on with our salt water pools. The following is what he sent me:

Before I start with this, I want to make sure you understand that I fault no particular manufacturer, but rather this applies to all products identified as "Salt Chlorine Generators" that produce sodium hypochlorite through the cell process. That is mostly because you don't have to look hard to find out who makes the cell plates for everyone. It just happens to be the same guys who make titanium exchangers for most heat pumps.

I have thought some on the step-by-step process where a pool can be checked. I guess the best I can say is that it is very situational, i.e. what components are on a pool, what level a generator is running at, length of grounding run to equipment, style of coping, and so forth.

I tested two pools yesterday that are built very much the same so that I would have a basis of comparison. Luckily, one was mine and the other was our lead technician who, up until recently, sung the praises of salt as "just too easy". I welcomed the opportunity to publicly tell him "I told you so" when he mentioned that his aluminum coping was starting to erode. His question to me after I had him do some extensive measurements on his pool, was please explain why my pool is doing what it is doing. I must have had a smirk on my face during the entire explanation, but I was glad to at least have a solid convert under my roof.

What we got yesterday was as follows. First reading is from his salt pool, second reading is from my erosion feeder pool:

Amps 0a 0a

This was not the norm, but it has been very dry and the ground wire was shallow.

DCV 480mv 10mv

Measured from water to ground

DCV 750mv 50mv

Measured from water to aluminum coping

ACV 380mv
Measured from water to ground

ACV 250mv 30mv
Measured from water to aluminum coping

Res. 5 ohms 500 Kohms

Measured from water to ground

Ohms 10 ohms 400 Kohms
Measured from water to aluminum coping

The point of these measurements is to give an indication of the "conductivity" of the pool. Since these pools were built in the same way, using the same materials, and I am pretty sure by the same builder, I think there are some clear implications. First, the only difference between the pools is that his has a salt system and mine a simple erosion feeder. I take no better care of my pool than anyone else and I also think that they were built at the same time.

What I always focused on was the DC voltage in the water and the resistance to ground. The higher the voltage (I have measured up to 1 volt in some cases) and the lower the resistance (2-3 ohms being the lowest) the faster the problems presented. Now I know that a quick student of ohms law would tell me that the higher voltage is due to a larger resistance to develop a "load" and that it should not be possible to have both a higher voltage and lower resistance given similar circumstances. However, there are other factors that would allow such an occurrence and they are far too complicated for this explanation.

Since the origin of the voltage is the cell (no matter what the manufacturer says) which to an average student of battery operation would conclude that starting at the cell, the current must migrate back to the source to complete the path. I think the builders of the cell would argue that the current is passing straight from one cell plate to the next in a closed loop at the generating cell. I guess I would just say then that perhaps the water rushing by the plates must "wash" some of the electrons out into the pool unintentionally and they just fall harmlessly to the bottom of the pool waiting to be vacuumed later. Clearly, under the best of circumstances, current will find multiple paths back to the source (path of least resistance notwithstanding). I am not implying that all the current generated at the cell is passing through the water. What we are talking about here is "stray" current that is not intentional. Otherwise the speed of deterioration would be much more dramatic.

Our experiences are not limited to vinyl. The problems are across the spectrum of pool construction and include concrete and fiberglass. The only difference is what is does to the particular surface material. What is common is what happens to metal components: Ladders that rust into nothingness, stainless niches that lose their conduit connectors, ground lugs, and niche rings, aluminum coping that starts decaying at the point where it meets the concrete, and so on and so on. I have ladders laying in the yard that look like they were processed in an electroplating bath. Then there are the countless pools that shock the users because some or all of the ground connectors are decayed into non-connection. Why? Current migration back to the source. However you want to define the process whether galvanic corrosion, electrolysis, (insert your type here), the result is the same. And in cases where the water carries a contaminant such as magnesium, the gray staining is also present.

In these cases, the gray color was pronounced on locations that would be most likely to allow current migration. Specifically, the stains were at the panel seams, wall bases, floors where the water jet forced water, etc. We actually sent liners away to labs to have spectrum analysis run on them to identify the stains. While we understood the items found, it took a while to connect the cause.

In all of these cases the common factor was a salt system. Now, we could not blame the units where the customer just let them do their thing without checking them from time-to-time. In those cases, when the chlorine got to 50ppm plus, it was hard to blame anyone else for what happened to the liner. That is when we found out that a liner can "absorb" half its weight in water under the right circumstances.

But like I said earlier, at least an erosion feeder would run out after enough neglect. What got terribly old through all of this was the manufacturers oft repeated phrase, "well I just don't know what to say, none of my other dealers are having this problem" or "I swear, it is only happening to you guys". This was repeated enough that we warned our reps that if they said that one more time, they could not return to the property--ever.

It has been about three years or so now and I am happy to report that our problems have gone away completely. I think it is no coincidence that it was about the same time that we stopped installing salt systems of any type. At this point, there is no sales person alive that could make an eloquent enough speech to convince us that the units are "fixed" and we would do well to "try" them again. That issue is dead for us and we won't even talk about it with anyone.

So, there you have it. Of course, the same old squeaky wheels out there – the Salt Reps – are going to say, “that’s just one builder. His findings don’t represent the whole industry”. And while that’s true, stop and ask yourself why his findings are the only findings available when there are reports nationwide about the very things that he and I are talking about.

Let’s face reality for a minute. These salt manufacturers are making boatloads of money selling you on the Joy of Salt, and the other half the industry is making a buck saying that all salt pools need sacrificial anodes because of incidence of staining, discoloration and metal deterioration – like Pool Tool Co and others. This is a problem. The whole thing is degenerating into a snake oil scam. The Salt Manufacturers are taking all this profit, walking away from all this damage, leaving the builders and service companies and other manufacturers of products destroyed by salt stuck with the liability for all this damage.

And the reason that research like what our friend has given us is the only research we can find is because the manufacturers already know that any real peer reviewed research that is performed will only point to the fact that they're baling water on a sinking technology; salt water chlorination through electrolysis.

And the proof is in the "companion products" being sold with salt systems. Pool Tool Co,on their own website, says that sacrificial anodes will stop plaster discoloration, metal erosion, heater damage and black stains around your pool light.

These are smart people at Pool Tool Co. They know that the problem exists. How can the manufacturers keep stonewalling and saying, “Nah, you’re seeing things”? Somebody’s lying to us. So when you show this handy dandy little procedure for checking for Stray Currents to your Salt Rep and he says, “No way. Stray Currents don’t exist,” tell him that he needs to get an injunction against Pool Tool Co then. Because the Salt Reps have already told us, it can’t be Galvanic Corrosion.

You see, the metals don’t touch,and we're only using 3,000 ppm, and you must have bonding issues, and you're using inferior grade stainless steel, and, and...
Oh, look. I've run out of excuses.

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