SWG source of chlorine

[max2k]

I would appreciate if someone could clarify where chlorine comes in SWG pools.

According to this: https://en.wikipedia.org/wiki/Salt_water_chlorination all chlorine comes from muriatic acid which would require its addition in the same amounts as chlorine. The salt concentration remains the same over time. Since MA is more expensive than Chlorine this would be significantly more expensive way of chlorinating water.

What am I missing here?

 

[needsajet]

Good question, covered in this thread: Pool Water Chemistry
See post #3, about halfway through that post for SWG chlorine equations.

The SWG uses any chloride ion, however the vast majority of them have come from the salt in the pool, and return to being chloride ions after use in the chlorine system anyway. I remember reading that Wikipedia entry (mostly poppycock) and it slowed down my learning as well.

 

[Griswald]

Salt is made up of sodium and chlorine. All the SWCG does is break some salt into its parts temporarily. The chlorine part is what we need. After a while, the sodium and chlorine go back together to keep the salt in the water.

Or there are tiny elves inside the SWCG and they all carry tiny bottles of Clorox.

Either way, as long as it works.

 

[JamesW]

When salt is added to a pool, the sodium and chloride separate and become individual ions. There is no actual salt NaCl other than very small amounts in equilibrium with the ions.

Chloride ions have 8 electrons in the outer shell. 8 is a full stable shell. As a chloride ion contacts the charged titanium plates in the cell, it loses an electron to become a chlorine radical with 7 electrons in the outer shell. Two chlorine radicals combine with a covalent bond to form chlorine gas. The chlorine gas dissolves into the water forming hypochlorite ions and hypochlorous acid. As the chlorine gas dissolves, one chlorine atom becomes chloride with 8 electrons in the outer shell and the other become ocl or hocl with 6 electrons in the outer shell of the chlorine atom.

As ocl or hocl oxidizes something, it takes 2 electrons from what it's oxidizing and the chlorine atom becomes chloride again.

The Wikipedia article is incorrect about needing to add acid. Once the correct TA is achieved, there should be no reason to add acid on a regular basis.

 

[Griswald]

When salt is added to a pool, the sodium and chloride separate and become individual ions. There is no actual salt NaCl other than very small amounts in equilibrium with the ions.

Chloride ions have 8 electrons in the outer shell. 8 is a full stable shell. As a chloride ion contacts the charged titanium plates in the shell, it loses an electron to become a chlorine radical with 7 electrons in the outer shell. Two chlorine radicals combine with a covalent bond to form chlorine gas. The chlorine gas dissolves into the water forming hypochlorite ions and hypochlorous acid. As the chlorine gas dissolves, one chlorine atom becomes chloride with 8 electrons in the outer shell and the other become ocl or hocl with 6 electrons in the outer shell of the chlorine atom.

As ocl or hocl oxidizes something, it takes 2 electrons from what it's oxidizing and the chlorine atom becomes chloride again.

The Wikipedia article is incorrect about needing to add acid. Once the correct TA is achieved, there should be no reason to add acid on a regular basis.

Nope...gong with elves��

 

[JoyfulNoise]

Does anyone have editor access to Wikipedia? If not, the article should be reported as containing incorrect information so that Wikipedia can either mark it as needing updates or pull it altogether.

 

[max2k]

When salt is added to a pool, the sodium and chloride separate and become individual ions. There is no actual salt NaCl other than very small amounts in equilibrium with the ions.

Chloride ions have 8 electrons in the outer shell. 8 is a full stable shell. As a chloride ion contacts the charged titanium plates in the cell, it loses an electron to become a chlorine radical with 7 electrons in the outer shell. Two chlorine radicals combine with a covalent bond to form chlorine gas. The chlorine gas dissolves into the water forming hypochlorite ions and hypochlorous acid. As the chlorine gas dissolves, one chlorine atom becomes chloride with 8 electrons in the outer shell and the other become ocl or hocl with 6 electrons in the outer shell of the chlorine atom.

As ocl or hocl oxidizes something, it takes 2 electrons from what it's oxidizing and the chlorine atom becomes chloride again.

The Wikipedia article is incorrect about needing to add acid. Once the correct TA is achieved, there should be no reason to add acid on a regular basis.

Thank you for the explanation. I went through the article in Pool School as well and it seems everyone agrees on electrolysis part, just present it slightly differently. Where Wikipedia article went completely off as you pointed out is the necessity to add HCl as part of the process.

I have 2 questions though:
1. If I understand SWG chlorination process correctly it leads to outgassing of H2 on regular basis. While it looks like something needs to be added to compensate at some point it seems later during 'consumption' phase of sunlight breakdown the O2 is outgassed as well so the net effect is H2O consumption, the rest of the ions Na+ and Cl- remain where they were before we began electrolysis. Is this correct?

2. For non-SWG pools it seems adding liquid chlorine causes accumulation of NaCl with time as oppose to SWG process. How significant is this effect? Can it be estimated how many gallons of 10% NaOCl does it take to raise NaCl concentration in 10,000gal pool by 1 ppm?

Thanks again for all the info, I'm contemplating switching to SWG but I'm concerned about constant pH increase reported by few members. My pool raises pH slightly on its own with liquid chlorine so I'm trying to guess how would it look like with SWG. My current TA is 60 from baking soda and pH raises at approximately 0.2 / week on average in 7.0-8.0 range. As you understand I don't want to end up carrying MA bottles instead of LC after the switch .

 

[Piolin]

I have the recommended TA level and borate, and my pH don't move at all, 7.8 all the time...

 

[JamesW]

Sodium and chloride are conserved. Salt is only lost by water loss other than evaporation and subsequent refill.

Salt systems do not raise pH; they are pH neutral.

1000 oz of 10% bleach added to a 10,000 gallon pool will add 129 ppm salt.

 

[max2k]

Sodium and chloride are conserved. Salt is only lost by water loss other than evaporation and subsequent refill.

Salt systems do not raise pH; they are pH neutral.

1000 oz of 10% bleach added to a 10,000 gallon pool will add 129 ppm salt.

Thank you! Looks like I added about 500 ppm of salt to my pool using LC over 1.5 years (about 150 gal of bleach). This doesn't take into account water loss besides evaporation. That loss took place as my CYA dropped from 300ppm to 60 so in reality most of that LC induced salt is probably gone.
Now I need to buy salt test to know exactly how much I have / need.

 

[needsajet]

Salt test strips are one of the few reasonably reliable test strips at +/- 400 ppm. After that, the SWG will tell you when salt gets too low, and you can add a bag. It's quite straight forward. If you like observing trends or anticipating, the Taylor K-1766 is a good test at +/- 200 ppm and easy to read the color change.

 

[max2k]

Salt test strips are one of the few reasonably reliable test strips at +/- 400 ppm. After that, the SWG will tell you when salt gets too low, and you can add a bag. It's quite straight forward. If you like observing trends or anticipating, the Taylor K-1766 is a good test at +/- 200 ppm and easy to read the color change.

K-1766 it is then, thank you!

I'm reading about various SWG systems and it seems Resilience A7 (305RES-A7) would fit my needs and provides good value but I don't see too many threads about it. Is there a well know problem with it which I missed or it's simply never got popular?

My understanding SWG provides maintenance supply of chlorine and should be sized to supply pool demand level within pump running time while manufacturers rate them based on 24hr continuous use. So if I have demand of 2ppm/day PoolMath requires 11 oz of chlorine to replenish over 8hr pump running time which is equivalent to 33oz or about 2lb cell for 24hr cycle. Is this correct?

 

[needsajet]

You've got it. A 2 pound per day chlorinator would deliver 2 ppm in a 44,000 gallon pool in 8 hours.

Another way to do it is to look at pool volume (44,000 gallons) times 8.35 lbs per gallon = 367,000 lbs of water. One part per million = 0.367 lbs. You want to be able to supply 2 ppm FC in your normal pump run time of 8 hours. So The SWG needs to produce 0.73 of a pound in 8 hours, or a bit above 2 lbs in 24 hours. A 2 lb SWG produces 0.083 lbs per hour. Most people average 2 to 3 ppm FC per day through the swim season.

I haven't heard of Resilience, so I'm no help there. You hear about these mostly here: Pentair, Hayward, Circupool and Jandy. Hayward doesn't make one big enough for your pool. If you want to go bigger, Circupool makes the biggest one. Economics are better as you go bigger because the cell lasts longer, but only helpful if you're going to live there ~5 years or more. If selling in a year, go the smaller/cheaper (but reliable) and the cell will be used up in a couple of years.

 

[rmturner54]

Good discussion. But for the avg end user. All I or they need to known is the salt cell when energized reacts chemically with the salt creating chlorine gas.

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[max2k]

Good discussion. But for the avg end user. All I or they need to known is the salt cell when energized reacts chemically with the salt creating chlorine gas.

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It doesn't react chemically otherwise plates would be gone by the end of day. Electricity is consumed to move chlorine from its 'passive form' to the active disinfecting one and I realized in course of this discussion nothing besides water needs to be added, only compensated for inevitable losses but the main process is chemically self contained and has 0 net effect. It also seems more realistic and predictable approach to size the cell based on max daily FC loss as it depends on particular pool and many of us know that number anyway: a pool needs to be brought in balance first using LC anyway, SWG can only compensate daily loss. SLAM still needs to be done using LC.

 

[txnole]

When salt is added to a pool, the sodium and chloride separate and become individual ions. There is no actual salt NaCl other than very small amounts in equilibrium with the ions.

Chloride ions have 8 electrons in the outer shell. 8 is a full stable shell. As a chloride ion contacts the charged titanium plates in the cell, it loses an electron to become a chlorine radical with 7 electrons in the outer shell. Two chlorine radicals combine with a covalent bond to form chlorine gas. The chlorine gas dissolves into the water forming hypochlorite ions and hypochlorous acid. As the chlorine gas dissolves, one chlorine atom becomes chloride with 8 electrons in the outer shell and the other become ocl or hocl with 6 electrons in the outer shell of the chlorine atom.

As ocl or hocl oxidizes something, it takes 2 electrons from what it's oxidizing and the chlorine atom becomes chloride again.

 

[rmturner54]

I think everyone knows what i am trying to say. So i will rephrase.
A voltage is induced to the salt cell plates and this reacts with the salt in the water. Thus creating chlorime gas.

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