Are you using an anode in your salt pool?

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eemueller

eemueller

LifeTime Supporter
May 31, 2013
61
SE Michigan
I'm curious if others with SWGs are using zinc anodes in their pools? I have no ladders or railings to protect, but I did just have a galvanized pipe plug (factory-installed by Pentair) come blasting out of the heater manifold when it corroded sufficiently to weaken the threads. I see anode units that are plumbed into the system and bonded to the main bonding wire, and zinc weights that are hung in the skimmers. I'm guessing the plumbed unit is more effective. Any experiences or advice would be greatly appreciated. Thanks.

Eric
 
You can see my post here about it - Plumbing a Zinc Anode - worthwhile on SWG Retrofits?

I personally don't believe they do anything useful except add Zn ions to your water and the Zn plates that people just throw into their skimmers that are attached to nothing at all are especially useless. If you truly wanted to protect your heater core, then the simplest way to do that is to add a zinc or magnesium sacrificial anode setup directly between the heater core and a Zn or Mg bar buried in the ground near it. But that arrangement only works to protect the heater core from external galvanic corrosion and does little to protect the internal copper surface of the heater core. The best method of prevention is chemistry related - keep your pool properly balanced at all times and never let the pH go lower than 7.2. pH is the dominant factor in metal corrosion.
 
While keeping the chemistry nailed is obviously important, the research I've been doing the last couple of days leads me to believe that good chemistry alone is not enough. My failed heater plug is evidence. My pH has never been lower than 7.5, and I take a water sample to a lab at the start of each pool season to make sure that my pH controllers are calibrated properly. Even with perfect chemistry and good bonding, there is an very small electrical current created by the dissimilar metals that will cause corrosion. For $80, I can install a zinc anode unit that will take the hit. BTW, after doing some reading, I also believe that the zinc weights in the skimmers are a waste of time. The unit I'm looking at is the Pool Tools 104-D (PoolTool Anodes- Manufacturer of specialty pool and spa tools). I spoke at length with the owner, and while I understand he's trying to sell his product, his statements were in line with what I've been reading. $80 seems like very cheap insurance to me.
 
That anode will work....sort of.

First off, I'd install it as close to the heater in the plumbing loop as possible and attach the anode copper wire directly to the bonding lug on the heater using the shortest possible run of wire. This reduces the path length resistance of the galvanic couple. If the lug doesn't accept two wires then you may need to get a split-bolt to connect it to the binding wire coming off the heater lug. Normally for a sacrificial anode you want it physically bonded to the thing that your are protected or otherwise as close as possible. You also want the area of the Zn to match the surface area of the thing you are protecting. If there's an area mismatch, you'll get polarization effects that will degrade the efficiency of the couple. This why these anodes don't do anything for in-ground steel pool walls. Finally, since the anode is not bagged, you'll want to install it with the Zn pointing down so that zinc oxide settles in the bottom of the unit and doesn't get sucked into your water stream. Unfortunately in a chloride electrolyte, zinc will polarize and want to form zinc oxide mostly. The zinc oxide is somewhat adherent to the Zn metal surface so if the anode polarizes sufficiently, it will become passivated and be rendered useless. You may need to pull the Zn slug from time to time to scrub it clean and expose fresh zinc metal.

Magnesium is a better choice for an anode material because it is farther away from copper and iron than Zn is but it is also more expensive.

Let us know how it goes.

FYI - I haven't had a chance to look at my heater plug yet but I'll let you know what I find when I do tomorrow.
 
Interestingly, the guy at Pool Tools said exactly the same things regarding 1) location & orientation of the unit, 2) bonding, 3) cleaning the anode. Since our pool season here in Michigan is relatively short, he suggested cleaning the plug at the beginning of each season, before the system is full of water. The suggested solution was 6:1 water/muriatic acid for 10-15 min to remove the zinc oxide. As for the bond connection, I've got a supply of split bolt connectors from other installations.

The size of the anode is something I saw in my research. I can easily determine the surface area of the anode plug, but it would be difficult to calculate the same for the cathode (heat exchanger, probe surfaces, these renegade pipe plugs, the main pump, etc.) However, based on the size of the heat exchanger housing, the exchanger itself is considerably larger than the zinc anode, so that will work in my favor.

When you say "steel walls", do you mean rebar in the gunite? If that's the case, I've got a ton of steel in there, but I know for a fact that it's in the bond loop. I saw multiple connections before the PebbleTec was sprayed on. The same goes for the lights and the deck mounts for the handrail, which is no longer installed.

I spent a fair amount of time on the phone with Pentair tech support today, and they were shocked when they saw the pic of that plug. They were also at a loss to explain why they had specified a galvanized steel plug for this heater. The plug closes a hole for an optional pressure relief valve, which I don't have. My bonding is good (last year I cleaned and tightened every connection), and I followed their installation specs to the letter. They claim they've never seen this before.
 
Surface area of sacrificial anode "optimally" should be 1.25X the surface area of the thing you are protecting and it relates to the current density of the galvanic couple. The weight of the anode is what determines how long it will last.

As for the steel wall comment, that's related to vinyl liner pool installations that use steel walls.

I just posted to your other thread. My plug is zinc, not galvanized iron.
 
I added a zinc anode driven into the ground right next to my heater. It's wired to a grounding lug on the heater. I don't know if it really does anything but I figure it couldn't hurt anything.
 
chiefwej said:
I added a zinc anode driven into the ground right next to my heater. It's wired to a grounding lug on the heater. I don't know if it really does anything but I figure it couldn't hurt anything.
Click to expand...

Move it to the bonding lug or attach it with a split-bolt to the bonding wire....You'll get a stronger placebo effect :p
 
Hi EE. My heater installer swears by Pool Tool and concurs with what pool tool and Matt say in terms of placement and bonding. Mine was installed late July retroactively and already looks oxidzed enough that I'll need to clean it soon. I don't know if that means anything at all in terms of whether its preserving my heater as heater is brand new and functioning right.

With that said, I pulled my side ladder on Sunday while working on a pool related project and to my dismay watched pure rust water drain from the leg into my pool when the cap fell off (and this after trucking in 24,000 gallons of iron-free water after a liner change last month ;( ) So the anode clearly did not protect an old stainless side ladder...but it may well have already been corroded inside the tubes, as my guess is that its 15 years old. Said offending ladder is headed for the scrap heap...I understand they make coated ones for swg use. Will go that route or will go without.

I know that's something of a mixed review, but for $80 and a bit of plumbing to protect a heater catastrophe I'd still do it...and did ;)
 

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JoyfulNoise said:
Move it to the bonding lug or attach it with a split-bolt to the bonding wire....You'll get a stronger placebo effect :p
Click to expand...
That is exactly how it's connected, and I think placebo may be the only effect it actually has. I'm thinking it may slow the rust on the heater's housing, but that's probably about it.
 
chiefwej said:
That is exactly how it's connected, and I think placebo may be the only effect it actually has. I'm thinking it may slow the rust on the heater's housing, but that's probably about it.
Click to expand...

I have a magnesium plate and all the ingredients for a proper bagged anode configuration (cotton bag, calcium sulfate, sodium sulfate and bentonite clay) and I plan on attaching it to my wrought iron fence to see how much weight loss occurs over a year. I'll also only hook it up to an isolated portion of the fence. We'll see if I can detect any difference.
 
JoyfulNoise said:
I have a magnesium plate and all the ingredients for a proper bagged anode configuration (cotton bag, calcium sulfate, sodium sulfate and bentonite clay) and I plan on attaching it to my wrought iron fence to see how much weight loss occurs over a year. I'll also only hook it up to an isolated portion of the fence. We'll see if I can detect any difference.
Click to expand...
Maybe check if there is a dc voltage difference between the anode and the fence?

You could also check for dc current.
 
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