Plumbing a Zinc Anode - worthwhile on SWG Retrofits?

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Swampwoman

Swampwoman

TFP Expert
LifeTime Supporter
Apr 27, 2012
3,765
Grand Rapids, MI
Greetings, all. Horse may be outta the barn as I already have someone installing this today with the new heater but Joyful Noise suggested I post in a new thread to discuss caveats of Zinc anode placement.

In my setup, the tech intends to plumb a t-style one inline between the filter and heater.

For the benefit of anyone interested in using sacrificial anodes, (and if in time, for my wn interest) what's correct placement versus incorrect placement and is this something worth doing when you convert to a swg pool?

(Note I am vinyl, ergo inline, that I realize I'm adding a bit of zinc to the water, that my new heater is cupronckel, and that my old copper heat exchanger developed a leak and obvious corrosion after switching to swg and having well-managed ph at 7.6...and that I'm on well)

-- So I'm banking on the cupronickel being key here, and the anode is just an extra precaution so if its useless or poses problems not worried about the sunk cost ;)
 
So, using my incredibly sophisticated, 2nd grade art skills, here's what you propose (in two pictures) -

E50F198E-2609-42E0-9B97-3C9DA72CCBF5_zpssdo3h8hm.jpg


And this -

490A57F0-DFD4-4480-97BD-2F3855C2473B_zpsr7cwrcsh.jpg


So, by adding a zinc bar to your water, you are doing two specific things -

1. You are creating a really lousy water bond;
2. You are intentionally creating a galvanic couple between your pool heater core (Cupronickel) and the zinc bar

I asked about a water-bond plate in your skimmer because, if you add that, you would then have two galvanic couples - one between the zinc bar and the heater and one between the stainless steel plate and the zinc bar. You can see from second cartoon what I mean by a galvanic couple. With zinc and copper (basically the same as your cupronickel heater, just slightly more cathodic), you will create an electrochemical cell that would, if the right ions are present in your water, cause the zinc to corrode and the copper to be plated with metal. However, in the absence of a divalent metal ion in solution that could plate out onto the cupronickel surface, the zinc will simply corrode a little bit and then "charge up" or polarize the cupronickel heater and keep it from degrading. The main problem with this is, as the solution chemistry changes (temperature, ORP level, pH, addition of metal ions, etc, etc) the amount of zinc that can be in equilibrium in the solution at any given time will fluctuate and so there will not be a constant cathodic potential on the cupronickel surface and the anode (zinc) will cyclically polarize and depolarize in unpredictable ways and thus always be a source of zinc ions in the water. Zinc also naturally has an equilibrium concentration of Zn2+ ions in water at about a 1ppm concentration (based on the solubility product and pH), so your water will be "contaminated" with zinc. Finally, a zinc anode needs to be designed so that the surface area ratio of the anode to cathode (Zn area/ heater core area) is slightly larger than 1 (typically 1.25 is a good starting point). This ensures that the Zn anode is capable of fully protecting the cathode. Another consideration which is overlooked is that the anode will shed material (zinc oxides and metal particulate) is un predictable ways. Anodes are always "bagged" to ensure that the "stuff" coming off of them is captured and not a source of physical contaminants.

Of course, this says nothing about non-galvinc corrosion that can occur just from having pH changes or chemical attack. That is entirely separate from the galvanic process.

Another thing to consider about point #1 is that you are now creating an electrical water bond where none existed before. Does the soil around your pool at 3ft out have a copper mesh that is connected to the bonding system? If not, then your pool water can now be at a potential different from the wet ground outside the pool and result in stray voltage...you can ask CowboyCasey all about his troubles with a water bond and no ground bonding outside his pool.

Honestly speaking, I don't believe these zinc sacrificial anodes afford you any more protection over the life of the heater core than simply following good chemistry practices. As for your experience of hooking up your SWG and then your heater developing a leak, I would say that is merely circumstantial and not correlated.

Your call, obviously, but I'm not a fan of the setup.

Matt
 
Thanks, Matt.

I think I need a better understanding of a few things.

My pool is inground, with cement surround and then a drain around the entire circumference (for drainage due to hill/terrace) covered with decorative stone. I wasn't the original owner at time of build. So I have no way of knowing about the copper mesh. Is there any way to tell? Is the mesh a standard construction practice?

FWIW, to date it seems the pool was built well at the time and according to pro standards circa 2001, whatever those standards may have been, with the less common addition of a deep end sump that's plumbed to the filtration system in the event of high rate of water runoff from the hill. So from a construction standpoint, it seems to have been well engineered. I am told the panels are composite, not steel. Would this lack of steel, tight footprint, and surrounding drain have affected their decision tree re copper mesh? We've never had any events to suggest a lack of correct bonding.

However, when the swg was installed, the bond wire was at the pump and extended from there to the swg panel. I did not see a bond wire running to the heater, unless it connects somewhere that is not visible to me. In this case, does that mean my water is not bonded?

And by skimmer plate, did you mean is my skimmer bonded or did you mean will I put a zinc plate in the skimmer? Since I'm inground, is there a way to confirm the skimmer is bonded if you meant the former?

Is there an easy way to test the bonding?

Update:

My installer is not coming until the end of the day today. While I assume he already picked up the anode Friday, which I'll pay for either way, your vote Matt, would be either not to install it, or to install it, see experimentally if the zinc corrodes at all, and remove then remove the zinc to interrupt the galvanic bond?

Re: coincidental timing of heat exchanger leak and swg installation...at 15 years of course its entirely possible this is sheer coincidence, but at no other time have I had a bit of blue-green copper "sand"-like substance come through the return on my steps.

That happened after using the Jacks Purple, which is supposed to clean swg cells. I knew it was copper but had stupidly assumed the Jacks was precipitating the trace copper from my water with the higher calcium this year, as my actual copper reading dropped down to .1, as has my iron now.

To keep my csi from being too negative I've actually allowed my ph to be much higher this year (but still under 7.8) than prior years with more metal control.
 
Hmmmm...not sure why I had in my head that you had an AGP but I did...oh well, no matter except the phosphate comment and Mr. Fish remain!

So just forget about the copper mesh. If your pool was built properly then I would just assume the bonding was properly done to code. Also, forget about the stainless steel water bonding plate, those are mainly for AGPs.

So if you're saying what I think you're saying, the heater is NOT BONDED??? That would be very strange indeed. There should be a bonding lug on the heater (separate from the green electrical ground wire) and there should be, at a minimum, a bare #8 Cu wire connected to it which runs back to the rest of the bonding systems. You might to explain this to Grodon (gwegan) and get his input...something doesn't smell right.

If your heater corer is un-bonded then is makes the Zn anode EVEN LESS effective because, looking at the second picture, it would be like cutting the connection wire between the Zn bar and the cupronickel bar. So at that point you wouldn't even have two dissimilar metals creating a galvanic couple....you'd simply have two pieces of metal in the same solution. Makes no sense whatsoever.

If you're really intent on having your plumber/electrician friend do the job, then maybe he can install the tee without the Zn bar and wiring attached until you can figure out what it is your bonding system is doing. My recommendation remains unchanged - I still think the Zn is effectively useless....

...but the placebo effect is well-documented in medical literature and shows that at least 30% of people will be cured with a sugar pill. Maybe pool heaters are the same - if you add a zinc bar they won't corrode.....hehehehehe....

Good luck,

Matt

PS - 15 years is a really looooong life for a pool heater. If I get 15 years out of my pool heater, I will be more than happy with that!!
 
Thanks - maybe I'll just pay him for the part (unless he can take it back to his distributor) and leave it at that. My main interest was getting the new heater hooked up ASAP but since he's plumbing shutoffs into the now-closed loop he'd asked if I wanted the sacrificial anode plumbed in at the same time.

Re: ABG - just thought it was easier to draw ;) If I were ABG, and had no fancy water table issues re terrace and hill, you can bet I'd have drained that sucker years ago re PO4 (and cartoon fish ;) (On that front, drain is imminent as new liner is ordered and just trying to line up installation to be post-roof project.)

When installer came out and looked at the job on Thursday, I told him I didn't see where it was bonded but that to count on bonding the Raypak and if needed extending the bondwire, which he said he'd bring just in case it was needed for extension. So the NEW heater will be bonded...perhaps there's something at the back that I can't see. I don't know if it makes any difference but my set up is inside a pool house (cement floor) that is on higher ground than pool, and the gas pipe and electrical panel that the boiler is on are separated, so maybe old code didn't require bonding for gas boiler if unit and piping were grounded? I can tell for example, that my light niche IS bonded (can see the box) etc. So it'd be kinda weird if heater was overlooked.

I agree that I feel pretty fortunate for 15 years of heater service, actually -- especially considering that thing sat with a total crashed TA and ergo 4.5 PH for two years during the foreclosure. I'm blessed it ran like a champ for a further 5 yrs!
 

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Sounds like bonding should not be a problem - just run a bonding wire from the heater to the pump or light niche bonding wire and you're done. Current code, as far as I understand it (which is not far at all), says that it all has to be bonded no mater where the equipment is.

Glad to hear the new liner is on the capital projects/improvements schedule. I guess the observatory is all done and your husband is enjoying some night time star gazing?

I'll keep my fingers crossed for the liner installation and when they pull out the old liner hopefully the pool structure is all good (no hidden surprises) ;)
 
Lol. Observatory location in plans has moved again and a certain someone is redrafting what he wants so we've separated the roof job (and pool) and I predict both are likely to be done before the observatory ;) It is now going to be an observatory atop a "bridge" shed structure that will connect between the "special" back garage and the poolhouse.

The redraft is kinda my fault in that after several nights atop a ladder trying to imagine the balcony observatory already quoted after both construction guy and roofer kiboshed cutting into the peak of the polebarn/poolhouse, hubby wasn't 100% in love with the predicted view through the canopy of trees. So I showed him where I thought he'd get maximum viewing and now he's working out a way to still be able to get his collector car outta the back garage and workout the stair configuration. Its tricky but doable, and it is for sure the next best sky access on our property, so it should all come together for him yet this season.

I just tend to be quicker on execution. Hubby is more methodical and some might say plodding. Which is fine unless his project is in my way ;)
 
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