Down side to SWG?

[Dirk]

The only downside of an SWG system is having to explain why it is the better choice for chlorinating a pool. Over and over. And over. And over...

 

[PoolStored]

The only downside of an SWG system is having to explain why it is the better choice for chlorinating a pool. Over and over. And over. And over...

And over...

 

[P00LNerd]

CSI and LSI - Further Reading

www.troublefreepool.com

I think there are some problems with that article, though. So, the study they mention at the top was being funded due to the amount of lead pipes used in water supply systems all over the country, namely in cities with larger and older public water systems, like Philadelphia. They were looking for a way to avoid having to change out all of the lead water supply plumbing, both by controlling corrosion (amount of lead leeched into the water) and by creating controlled mineral deposition as a means of safely encapsulating any lead present in the pipe or joint materials in a blanket of mineral deposits. I believe this method is still in use today, and would hope the methods used have improved, although you can still read about errors made in SI management leading to mass urban lead exposures among children in modern times.

So, we know that SI does play a role in metal corrosion, to at least some debatable degree. But then the author of this article goes and claims, "It also has nothing to do with metal corrosion, ie rust, although people and the industry routinely cite LSI as a measure of metal corrosion (that is simply wrong)."

Sorry, we know that statement is wrong. Maybe they meant to say it has less to do with metal corrosion than plaster, but it's hard to believe anything they write, after such a blatantly false statement.

Here's an opposing statement, with proper credentials and sourcing: "One measure of the potential for water to cause corrosion is the Langelier Saturation Index (LSI) (Langelier, 1936)." -- www.usgs.gov

Langelier Saturation Indices Computed for U.S. Groundwater, 1991-2015; Water Well Data and Characteristic Values for States

The occurrence of metals, such as lead and copper, in household drinking supplies can often be a result of the corrosion of pipes and joints in water distribution systems. One measure of the potential for water to cause corrosion is the Langelier Saturation Index (LSI) (Langelier, 1936). The LSI...

www.usgs.gov

Note they say "potential for", not "it will", indicating there are likely other factors not mentioned here.

 

[P00LNerd]

The only downside of an SWG system is having to explain why it is the better choice for chlorinating a pool. Over and over. And over. And over...

That's going to remain a battle, as long as there's an abundance of contradictory information out there, false or otherwise.

 

[P00LNerd]

The Taylor Watergram calculates LSI, not CSI. There’s probably a correction factor for TDS if you look into the math further. PoolMath CSI is a far better analysis of saturation index as it is based on actual calcite chemistry and not just fitting experimental data like LSI is.

Saturation index has very little to do with corrosion. It’s an old school misapplication of boiler water analysis adapted to pool heaters. Completely wrong. And, your heat pump heat exchanger is made of titanium (they all are unless it’s several decades old) and titanium is mostly immune to any chemical corrosion unless you’re pumping concentrated mineral acids through it.

Cool. I can believe that. Thanks!

What range do you guys keep for SI? Do you even track it at all? Does it affect build up rate on SWG grid?

 

[sande005]

Had tabs for almost 20 yrs. After my 20% pool drain for winter, this spring, the salt replacement was $28. With our heavy rains, and pumping out well over 1 ft of water, I'm now about 1 bag of salt low (still within generating numbers, just lower than my ideal target). So it needs about $7 in salt...if I bother.
I had a gal. of acid from last year. So my yearly chem expenses are looking pretty good, compared to before.....
And I only spend 15 min to 1/2 hr doing "pool stuff" each week.....
This will be the second 4th of July, EVER, where I was not spending many hours and $$ fighting algae.
Maybe next year I'll need some CYA after the drain.

 

[proavia]

The only downside of an SWG system is having to explain why it is the better choice for chlorinating a pool. Over and over. And over. And over...

THIS!
A thousand times........

 

[proavia]

Use CSI - it's already in PoolMath once you turn on track CSI.
And its computed automatically when you add the required test results.

CSI between 0.00 and -0.30 (negative 0.30) will minimize scaling in the SWG in a plaster based pool.
In your vinyl lined pool, anything below 0.00 is probably fine and will minimize SWG scaling.

You will want to test the salt level in your pool BEFORE adding any additional salt.

Add your test kit to your signature - and plan on getting the K-1766 salt test kit as well.

https://www.troublefreepool.com/account/signature

 

[P00LNerd]

Use CSI - it's already in PoolMath once you turn on track CSI.
And its computed automatically when you add the required test results.

CSI between 0.00 and -0.30 (negative 0.30) will minimize scaling in the SWG in a plaster based pool.
In your vinyl lined pool, anything below 0.00 is probably fine and will minimize SWG scaling.

You will want to test the salt lefel in your pool BEFORE adding any additional salt.

Add your test kit to your signature - and plan on getting the K-1766 salt test kit as well.

https://www.troublefreepool.com/account/signature

Thanks! Test kit is K-2006. Will add to my sig.

 

[P00LNerd]

Out of curiosity, I went hunting for some corrosion index or rate vs. salinity of water or salt spray, thinking it'd be interesting for the discussion. We know the Atlantic runs near 35k ppm, and our salt pools around 3.5k ppm. Most of us with boats or living in coastal environments know how things (even most stainless steels) corrode in this environment, but how does reducing salinity 10x affect that? With zinc-plated steel pool walls, and concrete paver surrounds, at some point salinity should matter.

Unfortunately, I didn't find anything easy or obvious for interpretation. But with all the experts here, I imagine someone has?

 

[JoyfulNoise]

There is no simple relationship between corrosion rates in metals and scaling indices in saturated (or under-saturated) water. Corrosion is a far more complex phenomenon than that as it depends on many other factors that we don’t measure (sulfate levels, nitrates, dissolved oxygen, etc) as well as the composition of the metal in question (different grades of steel have different corrosion properties). There just isn’t a simple answer other than “do the best you can to keep water away from the metal…”. You’re welcome to read through the articles over at Corrosion Doctors if you like -

Corrosivity of water and saturation indices

 

[proavia]

A chlorine pool is a salt pool and a salt pool is a chlorine pool.
Adding chlorine (liquid, tabs, granular) and muriatic acid also adds salt.
Many pools have a salt content of over 1000 ppm, some have a salt content over that required for a SWG.
This is why we recommend testing for salt PRIOR to adding any when installing a SWG.

Thousands of members with steel walled pools have a SWG without issue.
Tens of thousands more with concrete decks have a SWG without issue.
Honestly, in the time you've spent researching, reading and writing here, you could have had the system fully installed and be experiencing the benefits of a SWG. Don't over think it.

 

[JoyfulNoise]

Properly spec’d concrete will have additives in the mix that help reduce any harmful effects caused by chloride ions. It’s a fairly common spec especially in areas where there is snow and the use of de-icing chemicals on roadways. Sulfates are far worse than chlorides for concrete and steel which is why using dry acid is not recommended unless there is significant water turnover in the pool and rainfall around it.

 

[P00LNerd]

Not sure what's in this concrete, it's a colorized exposed aggregate specialty product, and very expensive compared to regular concrete. It's sealed with a good polymer sealer, which should last several years between applications, but of course that only seals the top surface.

I do know the same product was badly damaged by a prior owner using salt on the front walk, to melt ice, but there the salinity would have likely been 10 - 100x higher.

 

[Newdude]

I do know the same product was badly damaged by a prior owner using salt on the front walk, to melt ice, but there the salinity would have likely been 10 - 100x higher.

Ice melt remains behind when the snow melts and it can be millions per part, not parts per million. It's downright crunchy to walk on once the snows gone.

 

[YippeeSkippy]

Also, being new to liner pools, I'm not sure how often a liner failure is actually a leak. Don't they typically fail above the water line first, due to highest UV exposure there?

Just for the record- my first cell last >9 years. I'm on my second cell at 4+ years.

Also *properly* monitored/tested pool liners have been known to last 20+ years with pH neglect being on of the most common reasons for liner failure. High pH makes liners brittle.

Maddie

 

[P00LNerd]

Just for the record- my first cell last >9 years. I'm on my second cell at 4+ years.

Also *properly* monitored/tested pool liners have been known to last 20+ years with pH neglect being on of the most common reasons for liner failure. High pH makes liners brittle.

Maddie

What's your pH target? I've seen conflicting numbers, but I've been mostly aiming for 7.6.

 

[YippeeSkippy]

That's fine... its when liners go untested for months, years, so on and once tested are >8.2 or something weirdly low you've probly damaged it somewhat.
7.2-8max is allowable if it works within most folks entire chemical balance.

One common alteration common to folks in west or with extremely hard water fill water that can help minimize scale by keeping their pH on the lower end of acceptable pH. So it is sometimes desired lower than the range of up to 8.

 

[Dirk]

1. When I took over my pool (from the previous owner), there was no SWG. When I had one installed, the installer couldn't offer a reason why the salt content in the existing pool water was very close to what the SWG needed: upper 2Ks (neither he nor I understood that, without exchanging water, all chlorine pools build up salt over time).

2. I observed deterioration of my concrete deck near the grass, but none near the coping. And I also observed some deterioration to my coping (sandstone), but very much more so near the steps, almost none elsewhere. Both the coping at the steps and the concrete at the grass were subjected to much more water than anywhere else on the coping or deck. Basically, they were getting wet every day. Some of that water was pool water (with some salt), some of that water was city water (with virtually no salt).

My un-scientific (but real-world) conclusion: it's the water breaking down the coping and the deck, not the salt. Which could be argued, I suppose. But what's clear is the deterioration had/has nothing to do with the installation of my SWG.

For reference, there is no SWG installed at the Grand Canyon, but the water flowing through it has somewhat affected the wear and tear of the hardscaping.

 

[P00LNerd]

Thanks, Dirk. I think you're stretching a bit with the grand canyon, after all that little creek is moving nearly 100,000 gallons (+/- 40k depending on season) of water per second through that canyon. That's more than 4x the total volume of my pool, every second. Drag a bunch of the softest silk across stone at that volume and velocity for a few million years, and you'll have some deterioration.

But I follow you on the water and salt. As I said at the beginning of this tangent, I'm sure salinity matters, but the salinity here is very low, by comparison to anything else I've experienced, namely Atlantic sea water (10x higher) and salted sidewalks (10,000x higher). The only difference here is frequency of exposure is high. My goal will be to just ensure the concrete sealer stays in good shape, re-applying as needed.