Featured Pool Chemistry, stainless steel corrosion and prevention, long term study.

[ajw22]

That is as clear as ….

 

[PoolStored]

The description states “ Not recommended for Use in salt or brackish water”
Does that apply to a pool salt level that is 10% of an oceans?

Not as far as the salt part...
Saltwater is ~30,000–40,000 µS/cm conductivity.
"Freshwater" is <1,000 µS/cm
The pool is "brackish", but on the low end...~2,000–4,000 µS/cm conductivity.
Most estuarine environments are 8-20K

 

[JamesW]

Any weight change is directly proportional to the impressed galvanic current at the ladder.

So, what you're saying is that the more weight change, the more you will be impressed with the galvanic current?

 

[JamesW]

That is as clear as ….

The protection is based on the voltage differential.

Magnesium has a higher voltage differential, which means that it pushes electrons to the steel with more potential.

Corrosion of the steel happens when the steel loses electrons.

If the magnesium is pushing an excess of electrons into the steel, the oxidizer is reduced and the steel does not lose electrons.

 

[ajw22]

The protection is based on the voltage differential.

Magnesium has a higher voltage differential, which means that it pushes electrons to the steel with more potential.

Corrosion of the steel happens when the steel loses electrons.

If the magnesium is pushing an excess of electrons into the steel, the oxidizer is reduced and the steel does not lose electrons.

In simple language then … a magnesium anode provides more protection than a zinc anode?

You said it in post #18.

 

[PoolStored]

In simple language then … a magnesium anode provides more protection than a zinc anode?

Y.e.s.

 

[JoyfulNoise]

Why magnesium and not a zinc anode?

Either would work for galvanic protection but magnesium is the better choice from a practical consideration as it dissolves more cleanly and efficiently. Zinc has a tendency to passivate with an adherent oxide/carbonate layer making it less effective.

 

[ajw22]

Y.e.s.

I.like.simple.

 

[ajw22]

Either would work for galvanic protection but magnesium is the better choice from a practical consideration as it dissolves more cleanly and efficiently. Zinc has a tendency to passivate with an adherent oxide/carbonate layer making it less effective.

Why then are zinc anodes the favored use and recommendation among pool companies?

Cost?

 

[PoolStored]

Zinc anode production and material costs are lower per unit weight.

 

[PoolStored]

Ok, No more to report. Everbrite recommends a 2 week cure period before submerging.
Anode on order. I'll report in 2 weeks with first impressions and anode install.

 

[JoyfulNoise]

The price of magnesium fluctuates, but recent data indicates that the price of magnesium alloy ingots is around $3,340 to $3,500 per metric ton. For instance, in June 2024, magnesium alloy ingots in the United States were priced at $3340 USD/MT

The price of zinc per metric ton on May 14, 2025 is approximately $2,638.40. On May 6, 2025, the price was $2632.40 per metric ton.

 

[JoyfulNoise]

Magnesium is also a much more difficult metal to process as it is extremely flammable and burns very hot. Once a magnesium fire starts, it’s difficult to put out. Zinc is far less reactive and easier to work with. Both metals present inhalation health hazards when casting or machining them.

 

[ajw22]

Zinc- lower cost, easier to work, less flammable than magnesium.

Don’t sniff either one.

Got it.

 

[sande005]

Included in TDS.

The formula:

• Salt = (CH*1.1678) + (TA*1.6859) + (Borate*2.6976)

• Sodium = 23*((TA-CYA/3)*2/100 + CYA/129 + Salt/58.4 - 2*CH/100)
• TDS = CH*(40/100) + (TA - CYA/3)*2*(61/100) + CYA*(128/129) + Borate*(61.8/10.8) + Salt*(35.5/58.4) + Sodium;

So I assumed that "Salt" above in lines 2 and 3 referred to the product of line 1. Do we need to account for the NaCl level additionally, esp with SWCG's? Or is it not really a TDS item?

 

[mas985]

From what I understand RSI uses the same pHs as LSI but if we believe that CSI is a better estimate for calcium saturation than LSI, shouldn't the pHs in CSI be used for RSI instead?

CSI = pHa - pHs
RSI' = 2*pHs-pHa = pHa-2*CSI

If I use this formula and my logs over the last 20 years, the average RSI' is around 8 and my heater is also 20yo but it also has a cupro-nickel heat exchanger. The 20yo stainless steel railing doesn't have much in the way of rust either. There has to be more to this than just RSI.

 

[PoolStored]

There has to be more to this than just RSI.

I agree, I just don't know enough about it beyond what I wrote. The anchors are lead anchors with Galvinized lags. There ladder mounts are aluminum and the ladders are 316. Something is going on...lol

 

[mas985]

I agree, I just don't know enough about it beyond what I wrote. The anchors are lead anchors with Galvinized lags. There ladder mounts are aluminum and the ladders are 316. Something is going on...lol

Sounds just like my railings but mine are all above water level as well so only get pool water when someone gets out which probably makes a big difference.

 

[JamesW]

The Ryznar index was created by John Ryznar in the 1940s.

In my opinion, it is not based on any legitimate science and it probably has no value, especially for swimming pools.

It claims to be based on empirical correlation, but in my opinion, there is not enough good information to make a claim of empirical correlation.

Empirical means that it is based on observation and not on scientific principle.

The primary way it would provide corrosion protection for metal is from a buildup of scale over a metal surface, which can provide protection from oxidation.

The problem is trying to create a very thin uniform layer of scale without triggering a full scaling event.

Once you have a layer of scale, it provides a substrate for more scale to adhere to and the Index is already designed to create scale.

Maybe if you can get the layer to form and then balance the CSI you could maintain the layer without getting a runaway scaling event, but it would be very difficult.

For direct corrosion of metal, that is due to oxidation of the metal, which is due to something pulling off electrons like Oxygen or Chlorine or Galvanic Corrosion.

Stainless steel gets a layer of chromium oxide that provides protection.

Copper gets a layer of copper oxide, which provides protection from corrosion.

Low pH can dissolve the oxide layers and expose the metal to oxidation.

 

[PoolStored]

For direct corrosion of metal, that is due to oxidation of the metal, which is due to something pulling off electrons like Oxygen or Chlorine or Galvanic Corrosion.

I don't know enough about galvanic corrosion. Given the lead anchors, galvanized lags, aluminum mounts and SS, I'm sure something is going on. I doubt the anchors are bonded.

I'm going to try the Everbright first. If that doesn't work, I got the Mg anode and will try that.