Talk:Salt water chlorination

My new saltwater pool... I just moved into a new home and the electrolysis unit looks like it has not been maintained. Chlorine level in pool is near 0. A bit of algae growing. Will get pH to 7.0, clean electrolysis unit, add algicide and let you know how things go.

cyanuric acid is used as a stablizer for chlorine in outdoor pools only, because of the effect UV light has on chlorine.

As far as I know, there is no chlorine left in the pool when you're using a salt chlorinator. I've tested the chlorine level in my pool since I switched to salt and it registers no chlorine. The water is run through the salt chlorinator and returned to the pool as salt water. So the previous poster is incorrect about needing a chlorine stabilizer.Hcantrall 00:16, 22 June 2007 (UTC)

Your chlorinator is supposed to chlorinate. Are you measuring the chlorine in the water as it comes out of the chlorinator? If so and there's no chlorine the most likely causes are some electrical problem resulting in no voltage across the plates (check with a voltmeter), or calcium build-up on the plates preventing the salt water contacting the active (clean gently with acid), or overly aggressive cleaning with acid removing the catalysts on the surface of the plates (replace the cell). If you're measuring it later on, the lack of chlorine you're observing might be because in the meantime the sun's UV has broken down the chlorine too quickly because you didn't have enough CYA (cynanuric acid). The whole point of a chlorinator is (ultimately) to ensure enough hypochlorous acid to break down the cell walls of organisms smaller than you, the same goal as when using chlorine (e.g. trichlor) tablets. --Vaughan Pratt (talk) 05:49, 15 June 2008 (UTC)

The first paragraph of this page is utterly false - salt disassociates in water ... this is the lie the manufacturers tell you to smooth over the real chemistry that is going on (and that you don't actually have to buy those $1000 units from them).Bobxii 15:15 August 13 2007 CST

If that were true the salt would continue to work just as well after the electrolysis unit has completely calcified over, as it will in due course without proper maintenance. Have you ever seen a saltwater (6,000 ppm or less) pool without an electrolysis unit? For that matter have you ever even seen a saltwater pool? --Vaughan Pratt (talk) 05:16, 15 June 2008 (UTC)

What happens to the Na+ thats left over when the chlorine is used up? I have a salt waterpool and it hasn't gone solid with sodium metal yet after 10 years of use. 203.47.209.97 (talk) 21:38, 18 December 2007 (UTC) Allan

First off it won't be solid metal but sodium hypochlorite, sodium hydroxide, etc. Secondly any sodium not in a position to revert to NaCl due to loss of chlorine by e.g. evaporation will be backwashed out of your pool in due course. So you might get some build-up of non-NaCl sodium compounds, but only up to a point as the overall system drifts into equilibrium. It's a nice question what that equilibrium is, any pool scientists out there with a more precise answer? --Vaughan Pratt (talk) 05:30, 15 June 2008 (UTC)

I hope you wouldn't get Na+ in the bottom of your pool - Na is strongly hydrophobic! and strongly reacts with water when in the solid phase. I'm curious, if the pool water has 3,000 - 6,000 ppm salt, how is this less than the 35 ppt salt in sea water??? 35 ppt = ppm

35 ppt = 35,000 ppm, a lot more than 3,000-6,000 ppm. --Vaughan Pratt (talk) 20:12, 13 June 2008 (UTC)

I didn't think you'd lose salt via evaporation (water will evaporate, but the salt stays in the pool). Yet this article mentions that you lose salt because of evaporation. Is that really true?

The article mentions chlorine evaporating (which it does). Where does it mention salt evaporating (which it doesn't)? --Vaughan Pratt (talk) 16:50, 28 June 2008 (UTC)

Environmental Engineer here, I have little knowledge about salt systems, but they seem hotly debated. I am thinking that the electrolysis unit must pull alot of kWh, is that the case? I feel that this should be discussed in the article, to compare environmental impact to other pool systems.Shredthegnarbrah (talk) 15:12, 25 May 2010 (UTC)

No chlorine in salt water pool

The most common problem are the electrodes not work properly. They may need to be cleaned or replaced.

Article seemingly contradicts itself

The lead claims that the method "uses electrolysis in the presence of dissolved salt (NaCl) to produce hypochlorous acid (HClO) and sodium hypochlorite (NaClO)". But then the section on Operation claims that the method produces sodium hydroxide (NaOH) and free chlorine (Cl2), and that the NaOH drives up the pH, which must then be brought back down by adding muriatic acid (HCl) producing salt (NaCl) and water.

While these seem to be contradictory, what the article doesn't explain is that free chlorine reacts with water to produce HClO and dissociated muriatic acid in the form of hydrogen and chlorine ions. And perhaps the sodium hypochlorite arises in a similar way. Should some reconciliation be attempted here? (I'd do it myself if felt more confident about chemistry, I'm more into physics.) Vaughan Pratt (talk) 03:47, 8 April 2015 (UTC)

After reading a great many websites on this topic over the past 24 hours, I've concluded that if there is a website that explains the chemistry of pool chlorination both comprehensively and accurately then it has somehow managed to fly under Google's radar. It's as though either swimming pool chemistry was stuck in the 19th century, or everyone who understands it has taken a vow not to reveal only obfuscating nonsense about it online. Vaughan Pratt (talk) 04:09, 9 April 2015 (UTC)

Vaughan, see "Science-Based Swimming Pool Maintenance" (https://scithings.id.au/Pools/) or go straight to the details in the article "BABES: a better method than “BBB” for pools with a salt-water chlorine generator" (https://scithings.id.au/BABES.pdf). It explains the chemistry in pools with a salt-water chlorine generator with full referencing to the scientific literature. R Ge B (talk) 21:37, 14 April 2015 (UTC)

It is misleading in this Wikipedia article to say "Thus the consumable supplying all the chlorine is in fact the hydrochloric acid .... Net reaction : 2 HCl ---> H2 + Cl2 (as gases bubbling off)". In fact, chlorine gas is produced by electrolysis of NaCl in water. The chlorine gas is highly soluble, rapidly forming the sanitizing agent HOCl in water (it does not bubble off). So the net reaction in the electrolytic cell is: 2H2O + Cl- ---> HOCl + OH- + H2(gas). HCl has to be added to the pool because a proportion of the HOCl in the pool is consumed in reactions that do not perfectly balance the original production of hydroxyl ions (OH-) in the electrolytic cell. An example of the reactions that would (if they consumed all of the HOCl originally produced in the pool) perfectly balance the whole process (with only the loss of some H2O through bubbling off of hydrogen and oxygen gasses) is photolysis of HOCl: 2 HOCl <---> 2 H+ + 2 OCl- ---> 2 H+ + O2(gas) + 2Cl-. But any HOCl lost in pool overflow, or reacted with some organic compounds to be lost in volatile organo-chlorine products, does not return H+ (or Cl-) to the pool water; so most salt-chlorinator pool managers have regularly to add HCl to make up the deficit (i.e. to control rising pool pH). Acid may also be needed to counter rising pH from outgassing of CO2 if bicarbonate has been added to the pool as a pH buffer. Even so, the amount of chloride added as HCl is a tiny fraction of the amount from NaCl in a pool with an operational salt-water chlorinator. The sanitizing chlorine (HOCl) is overwhelmingly derived from electrolysis of chloride ions added in salt (NaCl), which also has to be replenished when it is lost in pool overflow. R Ge B (talk) 22:38, 14 April 2015 (UTC)

R Ge B I came here with the same thoughts. Please update the article. Tuntable (talk) 04:11, 15 May 2020 (UTC)

I agree. I think the article is skating over the chlorine chemistry and I’d like to propose the following stoichiometrics to resolve the issue.

4NaCL -> 4Na+ + 4Cl- Salt dissolves in water.
4Na+ + 4Cl- –> 4Na + 2Cl2 By electrolysis.
4Na + 4H20 -> 4Na+ +4OH- + 2H2 Reaction of metallic sodium with water.
2Cl2 + 2H2O -> 2HClO + 2H+ + 2Cl- Hydrolysis of aqueous Chlorine gas.
2HClO -> HClO + ClO- + H+ Dissociation of hypochlorous acid at pH 7.5 and 25C.
4NaCl + 3H2O -> 4Na+ + HClO + ClO- +OH- + 2Cl- + 2H2 Net of all the above.
Addition of Hydrochloric Acid to restore the pH to 7.5
HCl + 4Na+ HClO + ClO- + OH- + 2Cl- +2H2 -> HClO + OCl- +H2O + 4Na+ + 3Cl- +2H2.
NaCl +HCl +2H20 -> HClO + OCl- + Na+ + 2H2 Net of the last two.

So it seems to me that that considered in isolation, the free chlorine is contributed equally from the salt and acid, and both are consumed in the process. I think most of this chemistry is uncontroversial (and I hope correct !) but the following reference will help, particularly with the dissociation of hypochlorous acid. — Preceding unsigned comment added by Puntosaurus (talk • contribs) 20:19, 13 August 2020 (UTC)

I believe this is incorrect;

4NaCl → 4Na+ + 4Cl− Salt dissolves in water.

4Na+ + 4Cl− → 4Na + 2Cl2 By electrolysis.

4Na + 4H2O → 4Na+ +4OH− + 2H2 Reaction of metallic sodium with water.

The first equation is correct, when NaCl dissolves in water the ions will separate into Na+ and Cl-. But from here the sodium cation plays no part in any further reactions and for simplicity can be ignored. Electrolysis does not turn the sodium cation into sodium. The second equation should reed;

4Na+ + 4Cl- —> 4Na+ + 2Cl2 + 2e-. Two electrons move into the plate. This can be simplified by ignoring the sodium cations as;

4Cl- —> 2Cl2 + 2e-. By electrolysis.

Metal soldium does not exist dissolved in the water. The reaction of water and metal sodium is explosive. It is the sodium cation Na+ that is dissolved in the water but it does not take part in any of the electrolysis reactions and can be ignored for simplicity. Water gains an electron from the cathode to create hydrogen and hydroxide as;

4H2O + 2e- -> 2H2 + 4OH-. By electrolysis. 207.102.190.3 (talk) 17:27, 3 January 2024 (UTC)

Oxygen is also given off as a by product. If a membrane is used to separate the electrodes, separation of Hydrogen and Oxygen also occur. Andrew Romer (talk) 23:57, 18 November 2020 (UTC)

References

Incorrect Statements about Bromine

The last paragraph: Sodium bromide can be used instead of sodium chloride, which produces a bromine pool. The benefits and downsides are the same as those of a salt system. It is not necessary to use a chloride-based acid to balance the pH. Also, bromine is only effective as a sanitizer, not as an oxidizer, leaving a need for adding a "shock" such as hydrogen peroxide or any chlorine-based shock to burn off inorganic waste and free up combined bromines. This extra step is not needed in a sodium chloride system, as chlorine is effective as both a sanitizer and an oxidizer. A user would only need to "super chlorinate" or increase chlorine production of the cell occasionally. That would normally be once a week or after heavy bather loads.

This contradicts other Wikipedia articles that lists bromates as an oxidizin agent: https://en.wikipedia.org/wiki/Category:Oxidizing_agents Michaelassad (talk) 18:31, 21 August 2017 (UTC)

Electrochemical Chlorination.

The discussion surrounding the inventor of the residential salt water Chlorinator seems to be in dispute. I am not sure where the original sources came from. It would be interesting to see how they were validated by the original author. Following is some verifiable history.

Historically, Lindsay Isles, Len David, Ted Romer, Bob Joy, Bob Nowland and Ian Bevan were all linked in the early sales of what became of the Watermaid product. Len went on to create the "Clearwater" brand, Bob Joy initially sold Watermaid, later created the brand "Salt water pools" (that carried the Watermaid logo) then later "Aquajoy" Early on, Ian Bevan Sold the Watermaid brand but a dispute over the Watermaid name was held when Ian decided to manufacture his own product and attempt to use the name Watermaid. The Watermaid industries product was re branded "Aquamaid" after Ian failed to win the case. Other significant brands that entered the market like Lectronator. and..., There was a brand (name currently eludes me) that became Poolrite This model used a flappy paddle with a magnet and a reed switch to allow water flow detection. Possibly the earliest implementation of water flow detection in a Chlorinator. I repaired hundreds of them over time. Lectronator also used the flappy paddle (water pressure pushed the magnet on a paddle into the reed switch path to close the circuit) and there are still some product on the market today that use this (prone to failure) technique. Lectronator were ahead of their time back then with possibly the first reverse polarity unit to hit the market. As far as I am aware. Olin corp (chemical company) purchased Lectronator and paused the development to prevent Chlorine sale losses. Barry Gillings was a dentist and an inventor. He developed the Orsino Chlorinator and sold around 60 units which all ultimately failed. I repaired/modified a lot of them to allow them to continue operation as they were a robust power supply on their own. We added a Watermaid cell to them and they worked reliably for many years. The last one that I knew of still in operation was at the home of professor Ray and Lorraine Pierens in Carlingford. This was replaced in 2019. Barry holds some patents in the dental and other arenas. (he also plays the piano exceptionally well) I also have an original Watermaid unit in the reception area in our building that was installed in 1973 and taken out of service and replaced in 2003. Watermaid Industries (Ian Bevan) has since had it's registration cancelled (Oct 2019) When the name "Watermaid" was planned to become the product/company name, there was a meeting with Lindsay Isles, Ian Bevan and Ted Romer to decide the name. Ian left the meeting and immediately registered the name Watermaid Industries that day. Watermaid Pty Ltd was registered a few days later. Watermaid Pty Ltd manufactured cells for Watermaid Industries until the design changed around 1994 Watermaid also manufactured cells for the brand "Salt Water Pools" which also carried the Watermaid Logo.\ Salt water pools (Bob Joy) re branded to become Aquajoy. The Salt water pools unit was dominantly sold in Western Australia. (with the Watermaid cell) Transformers were manufactured by Radix, whereas the Watermaid transformers were manufactured by Industria.

Andrew Andrew Romer (talk) 23:54, 18 November 2020 (UTC)

The brand that eluded me is Aquanaught (may need the spelling of the name corrected) We saw one last year in here for repair. It had one of our electrodes attached and I had originally modified it to remove the flappy paddle and add a clipsal terminal junction box to allow the connection externally for the cell, possibly 20 - 25 years ago. It had no control mechanism and the rectification was a simple diode bridge. Maximum current for that unit was 15 Amps (rectified AC) Andrew Romer (talk) 06:14, 19 November 2020 (UTC)