Does an inline anode hurt?

[tenderfoot]

Hi,

I had never heard of a sacrificial anode, then I started to get some staining in my salt water pool (the cause is still undetermined) and I watched youtube videos and people saying YOU MUST have a sacrificial anode if you have a salt water pool or else!

Sooo.... I began my search here in TFP. And it seems that the consensus here is that they (anodes) don't do what everyone who believes in them think they are getting out of them.

I am completely new to this pool life, so I am kind of on the fence and thinking that IF the sacrificial anode (such as PermaCast TNIL20) doesn't actually do anything, but hurts nothing then I could just install one to have as insurance... You know... In case it actually does do something.

So, other than cost, would such a sacrificial anode cause any problems? Someone in one of the threads I read here asked about zinc being dropped into the water as the anode is being sacrificied and whether that is bad... Anyone got any information on all this? Thanks!

 

[JoyfulNoise]

Zinc is not very soluble in water and will almost always form zinc oxide (except at very low pH levels). The solubility limit of zinc ions is a few ppm’s at most.

The idea that you need a zinc sacrificial anode in a salt pool is not grounded in science. The people that push that stuff like to use lots of technical terms and information borrowed from the chemistry of corrosion science but don’t demonstrate much actual knowledge of how corrosion works or about chemistry in general. They are simply trying to sell you a product that will make you believe that it’s doing something useful when, in reality, it is not. That’s how pseudoscience and snake-oil sales work - make you believe that the product solves a problem that you may or may not have without any proof.

I’ve had a salt pool for years now without staining and without a zinc anode. According to their reasoning, my plaster should be full of stains and my heater should have rotted out years ago....but, amazingly enough, my “miracle pool” has resisted their iron-clad assertions of my impending doom! I guess I really must have magic fairies watching over my pool

 

[Bosley]

I was under the assumption that the sacrificial anode was to be used if you have a gas heater. The salt will corrode the the anode as opposed to the heater. Kinda the same ideas as in a hotwater tank in an RV. I am still in learning mode so don't take my word for it!

 

[bmoreswim]

I was under the assumption that the sacrificial anode was to be used if you have a gas heater. The salt will corrode the the anode as opposed to the heater. Kinda the same ideas as in a hotwater tank in an RV. I am still in learning mode so don't take my word for it!

I agree that is the thought process the OEM is usually going for. There is also a current discussion regarding a Fastlane swim current product that recommends an anode be used. Most previous discussions here have circled back to Matt's comments above on the topic.

 

[JamesW]

Magnesium Anode Extruded Rod 1.050" Diameter X Per Foot

[email protected]

www.rotometals.com

If you want a sacrificial anode, I would suggest a zinc or magnesium anode buried in the ground and connected to the bond wire.

The purpose of an anode is to provide an excess of electrons to the items that you want to protect. Items being protected are considered to be cathodes.

Things corrode because something causes them to lose electrons. This is called oxidation.

If you push electrons onto the cathodes, the excess electrons will be removed by the oxidizer instead of the oxidizer taking electrons from the cathode items.

A metal like zinc or magnesium easily loses electrons and will be oxidized by electrons flowing towards the cathodes.

You can even measure the dc voltage and current with a multimeter to verify protection.

As the anode gets oxidized, positively charged ions build up and can reduce the effectiveness of the anode.

So, it helps to have the anode in moist soil so that the positively charged ions can migrate away from the anode.

Some applications even use a dc voltage to improve the protection by increasing the voltage between the anode and cathode.

This is called impressed current cathodic protection. It's the principle behind powered anodes for water heaters.

 

[tenderfoot]

Thanks folks. I don't have a heater for the pool and there is no spa either. Just the pump, the swg and the filter... Like I said, I was really looking into the anode because of the videos I watched. I don't want to have zinc in the water at least not more than there may already be. So, I am gonna follow in Matt's (JoyfulNoise) footsteps.

 

[Neemer]

My builder installed one on mine, but it's location makes not a nickle's worth of sense to me. It's downstream of everything on the return plumbing.

 

[JamesW]

The point of the anode is to provide a source of electrons to the metal items that you're trying to protect.

The electrons flow through the copper wire to the protected metal (called a cathode).

The extra electrons go to oxidizers, like oxygen and chlorine to reduce them to harmless ions.

The voltage between the anode and cathode is one factor that determines how effective the anode is.

Sometimes an unintentional voltage differential can be present in a system.

If the voltage polarity causes the metals in the system to lose electrons, you will get accelerated corrosion.

If the polarity causes electrons to flow towards the system, corrosion will be reduced.

A anode provides a voltage with the correct polarity to provide protection and can help offset a bad polarity situation.

Magnesium provides the highest voltage of common anode metals.

The distance from the anode and cathode is also important.

The only reason that the anode is put in the water is to dissolve away the positive zinc ions as they are produced by the loss of electrons from the zinc metal.

If the positive zinc ions are not removed they reduce the voltage of the anode as positive charge builds up.

Note: The reason that aluminum anchor cups almost always corrode is that they act as an anode to everything else on the bond wire. Aluminum anchor cups should never be used around a pool.

 

[JoyfulNoise]

I agree with @JamesW on his descriptions of what happens. But, the proper layout and engineering of a sacrificial anode is far from simple and requires some proper calculations to make sure what you are installing will ACTUALLY work as-designed. For example, these are some of the many pitfalls -

1. Proper mass of anode - the mass of the anode determines how long it lasts and one derives a proper mass based on the surface area calculations one needs to do for the structural components involved. If the mass of the anode is too low, then it will not last long enough to afford protection.

2. Over-potential design. In order for an SA to provide appropriate levels of protection, the galvanic couple must exceed the corrosion potential of the metal being protected by a minimum of 300mV. As James points out, magnesium typically offers the greatest possible over-potential.

3. Anode area....it matters! If you couple a very large cathode (your pool structure) to a very small anode (chunk of zinc), the potentials involved might be correct BUT the current density at the anode will exceed its ability to dissolve or dissociate ions and you will create polarization of the anode.....which leads to....

4. Anode polarization. A chunk of metal does not uniformly corrode or dissolve away. What typically happens in most poorly designed anodes is that the surface oxidizes and then becomes non-conductive. Once that happens, you lose all catholic protection because the current flow ceases. For example, zinc in pool water creates a zinc oxide layer on the surface when it becomes polarized. Zinc oxide (and hydroxide) is a very poor conductor relative to the bare metal. The oxide will slough off over time but that’s not a given and so, shortly after installation, most inline zinc anodes will simply polarize (charge up) and you lose the cathodic protection. In soils, anodes are typically buried in anode bags (cotton cloth) with a mixture of sulfate salts and bentonite clay to promote continuous and highly soluble ion dissolution from the magnesium or zinc surface. If proper moisture control isn’t present, then the performance degrades.

And my all time favorite pitfall -

5. A closed circuit path!!! In order for any electrical circuit to operate, it must be a closed path - electrons must be able to flow or else there is no circuit. Many times when you look at how an anode is place in the pools “circuit” you’ll find that there’s no closed path. The circuit topology does not allow for electrons to flow (like leaving a light switch in the OFF state). So if there’s no closed circuit, how is the thing supposed to operate??

For those reasons and others, I simply can’t get on the sacrificial anode band wagon....I suppose like taking sugar-pills, if the placebo effect lets you sleep better at night, then go for it....

 

[JamesW]

I wonder if adding a dc power source would improve the performance of an anode?

Using a low voltage dc power source in the 2 to 10 volts range might provide extra protection.

Some water heaters now come with powered anodes.

Note: Adding a dc voltage to the equipment is not recommended unless it is provided by a product that is certified as safe for such use as with the powered anodes available for water heaters.

 

[duraleigh]

then I started to get some staining in my salt water pool (the cause is still undetermined)

I am not sure if you are interested in solving the stains or learning about anodes. If you want to work on the stains can you start by posting a set of current test results? We can help.

 

[tenderfoot]

Hi @duraleigh thanks. Yes, I will make a separate post about the stains. This particular post was really just about learning about the anodes.