SWCG pH increase

[dschlic1]

I had the chance over the weekend to test how much a SWCG increases the pH of the water. Once every month or so I back flush pool water through the air piping and then back into the pool. While doing this I place the SWCG into super chlorinate mode. I let the water circulate for about an hour to throughly clean out all of the spa piping.

Over the week while I was doing this, I had my pH meter out and decided to measure the pH of the pool water and also the pH of the water coming from the air piping. The water coming from the air piping was directly from the SWCG, running at 100%. The pH of the pool water was 7.45 and the pH of the water from the SWCG was 7.65.

So, in my case anyway, the SWCG increases the pH of the water in the cell by 0.2 pH units.

 

[JasonLion]

The rate of PH increase depends on your current TA level, higher TA levels means faster PH increase. If you lower your TA level to around 60 or 70 the PH increase should slow down dramatically or even stop completely.

 

[Strannik]

keep in mind that pH scale is non-linear
pH 7 is 10 times more acidic than pH 8, so even 0.2 increase is actually a big increase

 

[chem geek]

Remember that the chlorine output from an SWCG is similar to adding a hypochlorite source of chlorine (including bleach or chlorinating liquid) in that both will increase the pH upon addition to the pool. However, the consumption/usage of chlorine is an acidic process so the net result is not much of a pH rise. SWCG pools do tend to rise in pH over time, but it's not due from the higher pH of chlorine addition per se, but rather other processes we are still sorting out such as increased aeration of the water which has carbon dioxide outgas faster (which can be reduced by having a lower TA level) and with undissolved chlorine gas outgassing (so it doesn't stick around to lower the pH from dissolving in water nor from oxidizing something).

If it were not for these acidic effects described above, your pool's pH would rise by 0.2 units for every turnover of water, so probably by that much or more every day. That obviously doesn't happen. Same thing is true if you figure the high pH of hypochlorite sources of chlorine where the pool should rise in pH very quickly, but in fact many people (including myself) are able to have fairly pH stable pools.

 

[dschlic1]

Perhaps I did not make my point clear. I was trying to point out that I measured the pH change inside the generator cell. Nothing more, and nothing less. This should be of interest as one of the concerns (on a finer scale) is the CSI internal to the cell when generating chlorine. Now with some hard data, the CSI can be more closely pinpointed.

 

[JasonLion]

I would expect the PH increase inside specific spots in the cell to be much larger than that, and again it will be very dependent on the TA level of the water (and the borate level). Only a small portion of the water passing through the cell has it's PH increased significantly. Other water passing through the cell has it's PH reduced, and other water passing through the cell remains essentially unchanged. Then, as the water mixes together in the plumbing the PH moves back towards the average of all the water.