MAGNESIUM or ZINC

wireform

Silver Supporter
Aug 15, 2017
64
Spring Valley, NY
Pools in question are not the pool in signature:

Have two pools in question,

Pool #1 will be going over soon to SWG, it's vinyl and has a automatic cover with tracks below the coping with an above water header bar.
Pool #2 is currently SWG from a few years back , is vinyl and does not have a automatic cover so no tracks or header bar to speak of. I didn't see any sacrificial anode anywhere. Pool hasn't been opened for the last two seasons .Pump motor was just changed out because shaft was frozen with lots of galvanic corrosion on the back end of the motor. The rotary seal along with the other gaskets/seals where changed too. Looked like the rotary seal had been the culprit of the shaft issue with lots of galvanic corrosion there too.
I've seen much discussion about zinc and magnesium anodes and if I'm understanding correctly the magnesium is only necessary for pool #1 with the tracks and header bar made out if aluminum. I would like more clarification on what goes where such as zinc non bonded in the skimmer baskets and magnesium or zinc connected to the bonding wire, buried in moist soil next to the pad where the bonding is easiest? Are there any particular magnesium's or zincs better or worse for this purpose and is size of importance.
Thanks in advance, Allan
 
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mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
20,428
Laughlin, NV
Do a search of the forum and you will find the anodes are unnecessary. Most members do not have them and no issues.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
15,475
Tucson, AZ
The corrosion on the motor shaft is not “galvanic” corrosion but chemical corrosion - the leaking seal allowed water to get into the motor and that did the damage. The term “galvanic corrosion” only refers to corrosion that is induced when two dissimilar metals are in contact (eg, cast iron pipe connected to a brass fitting).

Check the materials and installation of the track. Is it aluminum or steel? What kind of screws were used to install the track? Often times the biggest culprit with autocover tracks are the screws - typically cheap steel ones in contact with the aluminum.

An unconnected chunk of metal sitting in the skimmer basket is useless. It does not protect anything. Sacrificial anodes need to be properly sized for the task at hand and directly connected to the thing you want to protect. Simply connecting it to the bonding wire of the pool is insufficient if there are multiple “things” connected to the bonding system. So if you want to protect the track, you need to connect the sac anode to the track as closely as possible.

If the track is aluminum, then magnesium is the only effective choice. The surface area of the anode needs to be as close to or larger than the surface area of the thing it’s protecting. Just burying it in soil is insufficient as well. Anodes need to be bagged in a cotton bag that is packed with a mixture of bentonite clay, sodium sulfate and calcium sulfate to ensure uniform dissolution of the magnesium and avoid anode polarization. The ground surround the anode needs to be kept moist, using an irrigation drip system helps.

As you can see, proper sacrificial anode implementation is a bit more complicated than what most internet suggestion imply.
 
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