Unlike other years, pH isn't naturally rising

[wayner]

My pool has a SWCG and the pool is open from May-October. In every previous year as the summer progresses the pH creeps up and I have to add MA. This year that has not happened, it has gone down a touch since my pool was uncovered a couple of months ago. Anyone have an idea why this would be? The only reason that I can think of is that we have had more rain than usual and I have not had to add water - after running the pool with water over the skimmer I actually pumped some water out. Could it be acidic rain decreasing my pH.

 

[mas985]

The only reason that I can think of is that we have had more rain than usual and I have not had to add water - after running the pool with water over the skimmer I actually pumped some water out. Could it be acidic rain decreasing my pH.

The rain could be acidic and the fill water can also be basic which it usually is. Combined, could mean that PH does not rise as quickly.

 

[JamesW]

Anode 4Cl^- -> 2Cl2.

Cathode 4H2O -> 2H₂ + 4OH^-.

2Cl₂ +2H₂O -> 3H⁺ + HOCl + OCl^- + 2Cl^-

HOCl + OCl^-+ uv light -> O2 + H⁺ + 2Cl^-.

Net reaction:

6H₂O + 4Cl^- --> 4H₂O + 4Cl^- + 2H₂ + O₂.

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.

For a SWG, you gain and lose the same amount on a continuous basis once you reach equilibrium.