What causes pH rise in pools with SWGs?

[Jimrahbe]

SWG's cause your pH to rise to 8.4

B,

Really??? How do you figure that? I have three saltwater pools and none have any automated acid injections and my pH stays relatively stable at 7.8.. I guess I need to tell them that they are all doing something wrong...

10 minutes a week is about all you need to ensure you pH stays balanced..

Thanks,

Jim R.

 

[Blue Fin]

Re: Looking for suggested for salt Systems

B,

Really??? How do you figure that? I have three saltwater pools and none have any automated acid injections and my pH stays relatively stable at 7.8.. I guess I need to tell them that they are all doing something wrong...

10 minutes a week is about all you need to ensure you pH stays balanced..

Thanks,

Jim R.

NaOH (Sodium Hydroxide) is the byproduct of generating chlorine from NaCl. It has a high pH.

 

[Donldson]

Re: Looking for suggested for salt Systems

NaOH (Sodium Hydroxide) is the byproduct of generating chlorine from NaCl. It has a high pH.

Yes, but chlorine usage is acidic, cancelling that out. Pools with newly installed SWGs tend to deal with rising pH because of the aeration in the cell. Once the TA is dropped to a level better suited for SWG pools (typically around 50) then less carbon dioxide will outgas and the pH will stay relatively balanced.

SWG chlorine generation is virtually pH neutral.

 

[Blue Fin]

Re: Looking for suggested for salt Systems

Yes, but chlorine usage is acidic, cancelling that out. Pools with newly installed SWGs tend to deal with rising pH because of the aeration in the cell. Once the TA is dropped to a level better suited for SWG pools (typically around 50) then less carbon dioxide will outgas and the pH will stay relatively balanced.

SWG chlorine generation is virtually pH neutral.

The pH of chlorine produced by a cell is 7.6 - 7.8 . Sodium Hydroxide (NaOH) which is also produced as a by-product pushes the pH up. Nothing is going to stop the production of NaOH.


Salt + Water + Electricity produces Sodium Hydroxide + Chlorine + Hydrogen Gas


Please explain "aeration in the cell". There should be no air in the cell otherwise a potentially catastrophic explosive condition exists.

 

[Donldson]

Re: Looking for suggested for salt Systems

Well, I just re-read my post to make sure but I just cannot find where I said that sodium hydroxide is not created. I said that chlorine usage is acidic. The sodium hydroxide that is created and the acidic reaction of chlorine reacting balance each other almost perfectly. This is the same reason using liquid chlorine to chlorinate is also pH neutral despite the pH of liquid chlorine being extremely high.

"Aeration in the cell" was a layman way to say that bubbles are formed and this allows CO2 to escape, raising the pH. As I said, this can be countered by running a lower TA level.

SWG chlorine generation is virtually pH neutral.

 

[JoyfulNoise]

Re: Looking for suggested for salt Systems

The pH of chlorine produced by a cell is 7.6 - 7.8 . Sodium Hydroxide (NaOH) which is also produced as a by-product pushes the pH up. Nothing is going to stop the production of NaOH.


Salt + Water + Electricity produces Sodium Hydroxide + Chlorine + Hydrogen Gas


Please explain "aeration in the cell". There should be no air in the cell otherwise a potentially catastrophic explosive condition exists.

SWG's are pH neutral. Hydroxide is created in the process but so is chlorine. All chlorine reactions are acidic so, when you consider ALL of the reactions involved, the chemistry is pH neutral, ie, just as much acidic hydronium (H3O+) is created when chlorine oxidizes bather waste or destroys pathogens as caustic hydroxide (OH-) is created inside the cell.

Aeration inside the cell is caused by hydrogen gas bubbles that are formed. The creation of those bubbles can capture dissolved CO2 gas in them and the subsequent loss of hydrogen gas at the returns (hydrogen gas does not dissolve in water to any significant extent) carries away CO2. The outgassing of CO2 causes pH rise because bicarbonate alkalinity in the water tries to maintain equilibrium and converts to dissolved CO2 through the consumption hydrogen.

You have had several posts recently where your chemistry comments are not accurate. Before you comment on pool water chemistry any further and since your are in the pool industry, I suggest you read these threads to educate yourself -

Certified Pool Operator (CPO) training -- What is not taught

Pool Water Chemistry

People naturally think SWG's cause a rise in pH because when they switch they go from having stable pH to having rising pH. However, they are attributing that pH rise to the wrong reasons. Most pool owners use acidic forms of chlorine (trichlor tablets and dichlor shock powder) and those acidic chlorine sources keep the TA and pH in check somewhat thus reducing the amount of acid needed to hold pH rise down. When they install an SWG and no longer use the acidic forms of chlorine, the pH rise increases and they need to compensate with more acid use.

The pH rise of almost all water systems is due to that fact that water has carbonate alkalinity in it. The pKa of the dissolved CO2/bicarbonate equilibrium is 6.5 and the pKa of the bicarbonate/carbonate equilibrium is about 8.4. Therefore pool water that sits right in the middle (around a pH of 7.6) will always have a tendency to rise toward a pH of 8.4 to satisfy the bicarbonate/carbonate chemical equilibrium. This is true regardless of the presence of chlorine.

 

[Blue Fin]

Re: Looking for suggested for salt Systems

SWG's are pH neutral. Hydroxide is created in the process but so is chlorine. All chlorine reactions are acidic so, when you consider ALL of the reactions involved, the chemistry is pH neutral, ie, just as much acidic hydronium (H3O+) is created when chlorine oxidizes bather waste or destroys pathogens as caustic hydroxide (OH-) is created inside the cell.

Aeration inside the cell is caused by hydrogen gas bubbles that are formed. The creation of those bubbles can capture dissolved CO2 gas in them and the subsequent loss of hydrogen gas at the returns (hydrogen gas does not dissolve in water to any significant extent) carries away CO2. The outgassing of CO2 causes pH rise because bicarbonate alkalinity in the water tries to maintain equilibrium and converts to dissolved CO2 through the consumption hydrogen.

You have had several posts recently where your chemistry comments are not accurate. Before you comment on pool water chemistry any further and since your are in the pool industry, I suggest you read these threads to educate yourself -

Certified Pool Operator (CPO) training -- What is not taught

Pool Water Chemistry

People naturally think SWG's cause a rise in pH because when they switch they go from having stable pH to having rising pH. However, they are attributing that pH rise to the wrong reasons. Most pool owners use acidic forms of chlorine (trichlor tablets and dichlor shock powder) and those acidic chlorine sources keep the TA and pH in check somewhat thus reducing the amount of acid needed to hold pH rise down. When they install an SWG and no longer use the acidic forms of chlorine, the pH rise increases and they need to compensate with more acid use.

The pH rise of almost all water systems is due to that fact that water has carbonate alkalinity in it. The pKa of the dissolved CO2/bicarbonate equilibrium is 6.5 and the pKa of the bicarbonate/carbonate equilibrium is about 8.4. Therefore pool water that sits right in the middle (around a pH of 7.6) will always have a tendency to rise toward a pH of 8.4 to satisfy the bicarbonate/carbonate chemical equilibrium. This is true regardless of the presence of chlorine.

You should contact the engineer at all the major companies in the industry perhaps even attend multiple seminars and training and tell the engineers and the instructors SCG's don't raise pH.

Almost as ridiculous as chlorine use is acidic cancelling it out.

 

[Donldson]

Re: Looking for suggested for salt Systems

EDIT: None of the following will make sense since the previous post was edited. I will leave it be but add one statement that I originally left out since it is regarding the only part of the previous post that remains.

Took you two weeks to respond and the best you got us "nuh-uh"?

Your understanding of basic chemistry is... troubling. Your claim to expertise is the same as saying the guy who pumps gas at a service station should be considered an expert in the field of internal combustion engines.

I, in fact, have been to several industry seminars. I have never been overly impressed with their knowledge and trust Matt far more when it comes to chemistry. On top of that, his post contains the actual chemical reaction information and your post is just an appeal to authority. I hope anybody coming across this thread recognizes who is presenting data to back up his statements and who is not.

I only wish I could say that your zealous adherence to incomplete knowledge came as any surprise. But, to paraphrase the great Rip Torn, "Congratulations, you're everything we've come to expect from years of pool industry training."