DIY Inline Anode

[diyindux]

I know these are subject to considerable debate here but I know the addition of one can't hurt. I figured if I could build one for a reasonable price, why not?

The commercial ones are $60 to $80 which seems ridiculous to me. The marine industry uses anodes on everything so I looked for something suitable there and found what is called a "pencil anode" which has an npt threaded cap and is for the cooling system. http://www.boatzincs.com/engine-sizes.html I picked up an E5 for $9 at a local marine supply place. I tapped the top for a 1/4 inch bolt and added a lug. I put a tee in the output from the pump with a 2 inch x 3/4 inch bushing and threaded in the anode. I connected it to the bonding grid and that was it. I'll need to check on it periodically to see if it is getting used up.

 

[Patrick_B]

Just out of curiosity, what is it made from? Zinc or Mag?

 

[diyindux]

It's zinc. The anode is replaceable and threads into the brass cap so a magnesium one may be available but from what I have read it will work.

 

[Patrick_B]

I honestly don't know which would be better in a pool system.

 

[chem geek]

Zinc is usually sufficient to protect metals in pool water. Technically, for protecting aluminum under some conditions magnesium might be required, but generally zinc is used and seems to work.

However, I think it would be better to connect the zinc anode to the bonding wire and to bury the anode in moist soil. With an inline anode, you are adding zinc ions into the pool water. Though they don't stain or precipitate as readily as iron or copper, they still can stain if their level gets too high or the pH gets high. The saturation level for zinc is roughly 2 ppm at a pH of 8.0 (see this PDF file for more details) though with metal complexes it may take much higher levels to actually stain or precipitate. The idea of a sacrificial anode is to put a small negative voltage onto the bonding wire that protects the other metals from corrosion. This occurs because zinc corrodes (gives up electrons) more readily than the iron, copper and aluminum it is protecting.

 

[diyindux]

I can add one there as well. A chunk of zinc bolted to a length of wire is pretty easy to set up.

Using a system with impressed current is the best, but that's a tough one to calculate. You need to size the array based on the mas of material you are trying to protect.

 

[chem geek]

There's no need to add both. If you are willing to put zinc into your water, then the inline anode should be sufficient for protection. The only reason to put it in moist soil is to avoid putting it into the pool water and having the zinc end up in the pool.

 

[diyindux]

Hey, maybe if there's zinc in the pool I won't need it in a daily supplement!

 

[toofast]

I am so confused...I am a bit of a marine expert on anodes, etc...and I totally understand WHY we do this with boats, but how does this anode help in the pool world. Normally you get galvanic corrosion between two dissimilar metals. In pool systems, what METAL parts are touching the water??

Perhaps the titanium in a heater ? If so, what is the other metal that might be giving up it electrons ?

Or is this trying to protect the titanium (or other metals) from stray currents ? But once again, unless you have a "short" that is flowing through a metal part, how can that happen in a pool system ?

I am just trying to understand....

 

[diyindux]

Any leaks in the liner brings the steel walls into the mix, as does splash over that gets under the coping. There is also stainless steel in the mix at the lights and ladder. I have a liner pool with steel walls and a swg so I know some corrosion is coming.

 

[toofast]

WOW - just never knew it was an issue with Pools...I don't have protection in mine, wonder if I am asking for trouble ?

 

[diyindux]

With fiberglass and chlorine I'd say you don't need to worry. If your levels are right and everything is properly bonded then supposedly I have no problems either but with the salt and all of the metals I'm a little nervous.

 

[toofast]

Gotcha...but I've learned something new today. Oh, any by the way, in theory there MUST be a way to test for this - I can use a special "silver chloride" cell hooked up to my meter to measure in millivolts the current in water, wonder how to use for a pool. Mmmmm.....

 

[chem geek]

It's not just dissimilar metals and galvanic corrosion. Steel hulls are protected by zinc sacrificial anodes (aka cathodic protection) as described in this link where you can see the zinc anodes directly on the steel hull. This isn't just corrosion at a boundary of dissimilar metals, but corrosion of the steel in salt water that is protected by the zinc being in electrical contact with the hull and being more corrosive so creating zinc ions into the water putting a negative voltage onto the hull which has it corrode more slowly.

In pools, there are several metal parts touching the water and these are all connected to each other with a bonding wire to force them to equipotential to prevent possibility from electrical shock in case there are any stray voltages. There can be metal in pumps, in copper or cupro-zinc or titanium heat exchangers in gas heaters, in stainless steel rails and light rings, and in screws.

As for measuring the corrosion rate or potential, you can try doing that but it would be challenging given the large volume of pool water. The risk for metal corrosion is higher when the conductivity is higher as is the case in saltwater chlorine generator pools that have around 3000 ppm salt. Also, the higher chloride levels in such pools can increase corrosion of stainless steel since chloride interferes with the reformation of the passivity layer.