Sacrificial Anode help

appstategrad

Well-known member
Jul 12, 2014
167
Hickory, NC
#1
I have a sacrificial anode that was installed when the pool was built in 2014. I've read varying opinions...some people think they are beneficial while others say not. I don't know anything about the type I have, how long they generally last, what kind of maintenance (if any) is needed, etc. When the time comes for replacement, is it a DIY or pro job?

The pic isn't the greatest because the outside plastic(?) has yellowed due to sunlight. Thanks!




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dradam

LifeTime Supporter
Mar 10, 2013
139
maryland
#2
I have a sacrificial anode in my swcg pool. Many companies sell them and some are in line and others can be clamped to existing piping, all attaced to your bonding wires. It is zinc and absolutesly becomes coated over the season. Per the manufactures instructions I remove it yearly and clean it to bare metal. I use an angle grinder but a file would do. When I loose too much zinc I will replace it, but that will take a good few years. In line or clamp on it is a realtivley simple DIY repair or replacement. I can't tell how to open yours from the photos, but it sure looks like it should be cleaned. I cant prove that it helps, but I would rather sacrifce the anode than have somthing else corrode. Hope this helps
 

appstategrad

Well-known member
Jul 12, 2014
167
Hickory, NC
#4
Thank you both! I'm not sure what the original diameter was. I was able to take closer pictures of the bottom part and I think I can get into it, but I'd rather have some additional info before I try. Thanks again!


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cjpwalker

Silver Supporter
Sep 1, 2016
173
Yakima, WA
#6
Thank you both! I'm not sure what the original diameter was. I was able to take closer pictures of the bottom part and I think I can get into it, but I'd rather have some additional info before I try. Thanks again!

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Looks like an o-ring between the white pvc and the black cap. I'd try to unscrew it if it were mine...
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,489
Tucson, AZ
#7
I am not a fan of these devices as I am of the (sound scientific) opinion that they are useless. At best you are simply corroding a chunk of zinc (forming yellow/white ZnO and Zn(OH)2 precipitates and coatings). Once the zinc bar becomes passivated, it no longer functions as an anode.

What precisely do you believe these devices are protecting you from? And, which part of your pool do you think you are protecting with something like this?



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cjpwalker

Silver Supporter
Sep 1, 2016
173
Yakima, WA
#8
I am not a fan of these devices as I am of the (sound scientific) opinion that they are useless. At best you are simply corroding a chunk of zinc (forming yellow/white ZnO and Zn(OH)2 precipitates and coatings). Once the zinc bar becomes passivated, it no longer functions as an anode.

What precisely do you believe these devices are protecting you from? And, which part of your pool do you think you are protecting with something like this?



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Galvanic corrosion. The zinc is attacked before the steel walls... For me it came with the pool build, so I'll keep in in. I know that I have seen 1" thick anode rods come out of water heaters that are now pencil thin, I have seen the sacrificial blocks on boat outboards and lower units badly worn while the rest of the metal is in good shape, and I have seen what happens when a copper water pipe rests on a black-iron fire sprinkler line. I have to think there is something to it.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,489
Tucson, AZ
#9
Galvanic corrosion. The zinc is attacked before the steel walls... For me it came with the pool build, so I'll keep in in. I know that I have seen 1" thick anode rods come out of water heaters that are now pencil thin, I have seen the sacrificial blocks on boat outboards and lower units badly worn while the rest of the metal is in good shape, and I have seen what happens when a copper water pipe rests on a black-iron fire sprinkler line. I have to think there is something to it.
Yep.

Except for the fact that, in order for metals to be used in that way, they need to be properly matched to application. When one wants to create a sacrificial galvanic couple, the surface areas need to be matched, in other words, the areas of the cathode (your steel pool wall) and the anode (your chunk of zinc), need to be equivalent. Otherwise you will completely passivate the zinc metal with a zinc oxide/zinc hydroxide layer and it no longer conducts current. The anode becomes "polarized" (which is just a fancy way to say non-conducitve and charged like a capacitor) and it no longer protect anything. At that point, the only thing that keeps the anode going is by mechanically disturbing the surface and hoping that enough passivation flakes of so that it can conduct again and develop an cathodic current.

In water heaters and boats, the placement of the anode is such that the water current is able to remove the passivation a bit and allow for it to act in a sacrificial manner. In most saline marine applications, one uses magnesium bars and blocks to protect outboards because magnesium is a better sacrificial material. In buried steel tanks, one usually bolts or welds many zinc bars onto the tank to help protect it; for critical applications, you actually use an impressed cathodic current protection (ICCP) system. ICCP systems are powered electrical devices that actually supply current to the thing they are protecting to keep oxidation from occurring.

The chunk of zinc sitting in the bottom of a PVC well with pool water flowing above it is barely doing anything at all except slowly rotting away and probably protecting the first few feet of bonding wire that is buried underground. And that's the other thing, not only is a steel wall hundreds of times larger in surface area than the bar, the wire connecting it is usually very far away which limits it's performance as an anode. Sac anodes, like surge protectors, are point-of-use devices - they work most efficiently when they are bolted to the thing they are protecting.

Unfortunately, this is just another one of those pieces of "pool equipment" that are added on to a pool because there some underlying "science" associated with them that is not at all matched to the actual application. Like UV disinfection lamps and ozone generators, these devices do something but the something they do is not necessarily significant. You could completely remove the device tomorrow and, over the years, not ever notice a difference.
 

cjpwalker

Silver Supporter
Sep 1, 2016
173
Yakima, WA
#10
Well that sucks... Lol

Appreciate the info. Glad I didn't actually purchase the thing separately.

So is there a way to effectively protect my pool?

I've heard of running a current before - I manned a shovel one summer in college for the gas company, and they use that process where they are still using steel pipe.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,489
Tucson, AZ
#11
For an inground pool with steel walls, there's not much you could do after the fact. You would ave to dig down or otherwise find a close attachment point to make a connection. The way to properly create a sacrificial ground anode is to bury several zinc bars attached at equal intervals around the pool. You then typically bury the anode in a cotton bag that is filled with a solid electrolyte. A standard formulation is to create a 2:1:1 mixture of bentonite clay:sodium sulfate:calcium sulfate you bag the anode with the clay inside the bag and the anode as well. The solid electrolyte is there to make sure that the zinc does not get polarized and allows the zinc to dissolve form the anode at a uniform rate. The sulfates create a slightly acidic environment and the sodium ions help to stabilize the zinc surface so that the zinc can dissolve as Zn2+ cations and not immediately turn into zinc oxide or zinc hydroxide. The bentonite clay provides a way of keeping the solids around the anode moist be retaining water. The bag should be buried in moist soil where it gets water form time to time, so near a drip system or some sprinkler that might hit it.

Zn anode bars for these types of application are usually several feet long and a couple of inches wide. The surface area determines the maximum current density that the anode will experience which is directly relate to the reaction rate. The total mass of the anode will dictate how long it will last. There are lots of tables online which can give you a feel for the size and weight of anodes needed for an application.

Bottom line is this - it A LOT of zinc....
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,489
Tucson, AZ
#13
If I could fix everything in life with some pieces of twine, chewed bubblegum and a bottle of aspirin, I'd be MacGyver and life's problems would be wrapped up in neat little 45min segments...sadly, I'm no MacGyver...

I'm sure your pool will be fine...


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cjpwalker

Silver Supporter
Sep 1, 2016
173
Yakima, WA
#14
If I could fix everything in life with some pieces of twine, chewed bubblegum and a bottle of aspirin, I'd be MacGyver and life's problems would be wrapped up in neat little 45min segments...sadly, I'm no MacGyver...

I'm sure your pool will be fine...


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I believe MacGyver's powers were derived from a combination of mullet, windbreaker, and cheese. All three can still be had, but getting the proportions right is the challenge...