Monday, August 20, 2012

Call Me Crazy: Zinc Balls & High Current Flow

I took most of the summer off this year. It was great. Not only did I get away from the Texas heat, but I spent most of the summer in a city that has very few swimming pools - San Francisco. It was great. Foggy and cool, or sunny and cool, or windy and cool. It was cool.

Then I came home. It was over 100 degrees every day for about the first ten days I was back. Got me all tuned up and back in-the-mode again.

Two things caught my eye after a summer of not thinking much about anything but walking up and down hills and not sweating. The first is this pic I snagged at my local pool wholesale supplier:


Notice the little black sign? SALTWATER PROBLEMS? Sacrificial Zinc Anode. They put stuff behind the counter for easy access to their higher volume articles. They have a whole warehouse of merchandise for sale, and about one hundred square feet of display space behind the counter, and right in the center of that display area are sacrificial zinc balls.

I wrote about zinc balls WAY BACK HERE. It was one of the first pieces I wrote, back when everyone was saying, "the Poolguy's  crazy, but you might want to put some Zinc Balls in your skimmer baskets, anyway".

If you look at that photo again, let your eyes wander down from that sign to counter top level, and then over to your left, and you'll see another item for sale on a blue card, it's another variety of sacrificial zinc anode. This one is meant to be installed in the plumbing line so that it has direct contact to the pool's bonding grid. In fact, if you go to POOLTOOL.COM, you'll see that Saltwater Problems have turned into big business for this company. Clearly, their top-selling items are Salt Pool related.

That's really the Smoking Gun, you know, attaching to the bonding grid. That's the same as an admission that Stray Currents are amplified and made much more destructive by these Salt Systems. That's why they want you to attach a sacrificial zinc anode to that grid; to put the least noble (softest) metal out there to bear the brunt of damage from the Stray Currents riding on your pool's bonding grid. The truth is your non-salt pool may have Stray Currents on the bonding gird as well, but you don't have highly conductive salt water to amplify the damaging effects.

Too, there's a chance that the units themselves could introduce Stray Currents onto your pool's bonding grid. No one's really done any testing to see.

Anecdotally, there's the recent article in Pool & Spa News that a salt system manufacturer is suing a pool equipment distributor for breech of contract; not paying for salt systems they received and resold for installation in people's back yard. You know, like YOUR back yard. The distributor explained that the reason they didn't pay was that the systems were faulty, in that they MELTED DURING OPERATION.

Hmmm... don't you hate that when your salt system melts down? It's better than having them EXPLODE, but only a little bit better. One of the installing company was quoted in the article as saying, "They are melting... It's a huge safety issue... I'm afraid someone's going to get hurt. It's a public safety hazard".

Turns out the first installing activity quoted in the article has installed "more than 200" of these systems in people's back yards, and now they're worried that the systems WILL MELT. The article doesn't indicate whether this company has notified these customers about the potential hazards in their back yard.

I'm betting not.

Another company had installed about 40 units, and when failures - READ MELTED SALT CELLS - topped 25% of installed systems, they yanked them all out of their customer's back yards and discontinued sales of the units. So, they're the Good Guys in the story.

Use the link above to the P&SN article and you can see a picture of one of the char-broiled salt cells. If you recognize it as something like what you have in your back yard, RUN!

You see, with most Salt Systems, you're running something less than 20 amps, but not much less. I know 20 amps because the cell fuse for a Goldline AquaRite is a 20 amp fuse. Leave a little + or - room, and you've got somewhere around 15 to 18 amps going through that cell on an average day. If I remember my old safety courses from the Navy, it takes 100 milliamps (one tenth of one amp) to kill you, so this is about 150 to 180 times the current requirements to kill someone. So it's easy to see how it would melt the salt cell. The company who makes this stuff admits that the salt cells melt, but blames it on the installers, saying they didn't properly connect the brass pins to the salt cell, allowing them to overheat and cause melting of the plastic salt cell housing.

The reason they heat up is because with a faulty connection, you have more resistance to current flow. The argument for the safety of putting 20 amps into the water is that with very little resistance between the cell plates, you never have any Stray Current leaking out via other, higher resistance paths to ground. But as you increase resistance to the current flow through a faulty connection, and you have a power supply capable of putting out 20 amps max, you basically have a recipe for disaster.

My blog is full of incidents of pool owners feeling a "tingling" when they grab a ladder or a side rail at their pool. That's Stray Currents, amigos.

I still marvel that we're having a discussion about the advisability of putting a known corrosive (salt) into pool water and then whacking in with something near 20 amps of current flow to save a buck on chlorine tabs.

Call me crazy...



Comments:
Hello Steven,

Is there a way I can contact / email you in a non-public way? It is about salt pool problems.

Thank you!

Russell
rcrcrcguy (at) yahoo.com
 
Yes, Larry. You can e-mail me at thepoolguy11 at aol dot com. I do it that way so the spambots don't mass e-mail me.
 
Adding a sacrificial zinc anode to the skimmer basket is absolutely pointless and only results in zinc getting oxidized by chlorine into zinc ions in the pool that could potentially stain. The proper use of a sacrificial anode is to ELECTRICALLY connect it to the metal you are trying to protect and to GROUND the anode usually by placing it in moist soil. What this does is to put a small negative voltage onto the metal you are trying to protect. This reduces the rate of corrosion of that metal.

So you are SUPPOSED to connect the zinc sacrificial anode to the bonding wire if you are trying to protect all metal that is in contact with the pool (which, of course is all supposed to be connected to the bonding wire). This has NOTHING to do with stray currents. Just having the higher salt level in the pool even without any saltwater chlorine generator would be enough to increase metal corrosion rates due to the higher conductivity. Also, specifically for stainless steel, higher chloride levels directly interfere with the reformation of the passivity layer which leads to faster corrosion of the underlying steel (iron).
 
I don't know why I find your posts so annoying. After all these years, you'd think I'd be used to you knowing just absolutely everything about everything with Absolute Certainty. I bet you sit in the first pew at church.

But I never do get used to it. I think it's the way you say SUPPOSED to, and NOTHING - as in, sacrificial anodes have NOTHING to do with shunting stray current corrosion.

Do me a favor. You live near the ocean. Go find a marine electrician and ask him if what you posit here is true. Then come on back. Your Humble Pie will be waiting for you.
 
I didn't mean that grounding won't shunt stray currents, but my point is that you cannot conclude that the reason that zinc sacrificial anodes are needed is that an SWG is producing stray currents. The zinc sacrificial anode is useful to reduce corrosion rates even when all that has happened is that the pool water has a higher level of salt so has higher conductivity and chloride — no extra stray currents because there is no SWG.

Zinc sacrificial anodes are used in marine environments to prevent corrosion not so much from active stray currents as from dissimilar metals for galvanic corrosion or from direct corrosion of a single metal (such as steel) in the conductive salty ocean environment.

http://www.cathodicme.com/sacp.html
 
Hi Steven,
I was about to install a saltwater generator next summer in my 15 years old pool until I read all your warnings and information. I am a ships engineer and should know all about salt water and corrosion and do agree with you. Ships have Zinc mounted all around the hull to avoid corrosion. I live in north Dallas with a 25K gallon pool, maintained with a DE filter and chlorine, Uses muritic acid for PH control and my pool looks great with super clear water.Water is hard in Denton county and expensive to soften and why I also saw ECOsmarte Pool Systems that uses glass media in filter instead of sand. Do you have any experience with those? Are they great or just another scam and expense. They also say you do not need any chlorine to maintain the pool. I will re-surface my pool in January due to plaster start getting worn out and was thinking about pebbles instead of the regular plaster. What do you think about that?
Appreciate and enjoy your blog and never seen so much facts any other places. Thank you for your time Bjorn Johnsen Highland Village
 
Hi Bjorn,

If your pool is fifteen years old, then the main thing to look for before you install that salt system is how much metal you have in your filtration stream. If you have a stainless steel filter tank, then it's a No Go. It'll rust through that tank in less than a year.

If you have a heater, then it's a Maybe. The salt will age your heater about three times faster than normal. So a heater that would normally last about 10 or 15 years will last about 3 to 5 years before salt damage starts showing up in failed components; like hi limit switches, pressure switches, or the whole heat exchanger. That's why companies like Hayward changed their whole heater line over to cupro nickel from copper to stave off salt damage and the flood of warranty claims on their heaters when they also became the number one company pushing salt systems on everybody.

The next thing to look at is your hardscape; what type of rock or concrete you have around your pool. If you have old concrete bullnose coping or brick coping and some type of concrete decking, then you probably won't notice much difference. If you have high end limestone, or any of the sandstone type flagstone - like Oklahoma flagstone - then you'll definitely see damage begin to occur the first swimming season, as the splashout evaporates and the salt penetrates the hardscape, eventually recrystallizing and causing damage to the stone from the inside out.

Finally, there's the environmental aspect. You're creating a reservoir of brackish water in your back yard. If you have to drain and refill just once on a 20,000 gallon pool, it will take 256,000 additional gallons of zero salinity water to dilute your discharge down to the EPA mandated level of taste (250 ppm). Here in Texas, whenever our reservoirs start to get low during drought seasons, one of the first problems they have is that the salinity level of the reservoirs starts to climb as the saline heavy treated discharge that replenishes them drives it up. Less water to dilute the effects.

But you'll have really soft skin and your eyes won't burn. So, by all means, blow all your money repairing your pool from the ravages of salt and destroy the environment while you're at it.
 
PS to Bjorn,

Don't know much about Eco Smarte, but Lew Akins does. He's a builder in the Hill Country and he started using Eco Smarte systems after he got burned replacing Limestone coping and decks on warranty when he got suckered into selling salt systems when they first came back around this time.

Check him out at lewakins dot dom.

And yes, I like pebble tech. It's a rougher surface that's more prone to algae. But if you brush your pool every week in the swimming season, and maintain your water chemistry properly, you'll like it too.
 
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