It is a myth that SWGs cause pH rise.
Anode 4Cl
- -> 2Cl
2.
Cathode 4H
2O -> 2H
2 + 4OH
-.
2Cl
2 +2H
2O -> 3H
+ + HOCl + OCl
-.
HOCl + OCl
- + uv light -> O
2 + H
+ + 2Cl
-.
Following the process, we can see that there are 4H
+ and 4OH
- created, which nets out to pH neutral.
The chlorine gas generated is very acidic and creates 3 hydrogen ions for every 4 hydroxide ions created.
As the hypochlorous acid is broken down by UV, 1 more hydrogen ion is created for a net neutral result.
Assuming that chlorine gain and loss are equal, there's no pH rise.
However, there is hydroxide generated in the cell, which can cause scaling due to the production of calcium carbonate.
Ca
2+ + HCO
3- + OH
- --> CaCO
3 +H
2O
If you have B(OH)
3 (Boric acid) in the water, it buffers the pH change by taking some of the hydroxides as the pH rises.
Borates to contribute to the TA (Total Alkalinity), but their most important role is in providing Total Acidity, which is the resistance to pH rise from added base (Like hydroxide), whereas total alkalinity is the resistance to pH drop from added acid.
Ca
2+ + HCO
3- + OH
- + B(OH)
3 --> Ca
2+ + HCO
3- + B(OH)
4-
Reducing the TA means that there is less Carbon dioxide, bicarbonate and carbonate in the water.
Carbon dioxide causes pH rise as it offgasses.
Bicarbonate and carbonate can create scale in the cell as it produces chlorine.
The general pool industry way overestimates the need to have TA as a buffer to pH change.
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