SWG pH rise

[POOLGOON]

I've read a couple of different things while browsing the forum in hopes of finding a clear answer.
The first is that a rise in pH comes from increased aeration of the pool water, thus gassing of carbon dioxide.
The second is that a byproduct of electrolysis (for NaCl water) is Sodium Hydroxide, which is a base.
I don't know if the NaOH is significant enough to change the pH, but it seems possible.
Or maybe it is a little of both?

 

[JasonLion]

The chemical reactions that takes place because of a SWG are net PH neutral (except for chlorine outgassing, which should not be happening). There are quite a few of them, some of which are basic and some of which are acidic, but overall there is no net change in PH. There is an advanced chemistry article in The Deep End that runs through the whole process, go here and search for "pH Rising" and also follow the equations link.

A SWG creates lots of little hydrogen bubbles, which are usually quite effective at aerating the pool, even when you can't see them. Aeration encourages CO2 outgassing if your TA is at all high (i.e. much above 60ish). That is what causes the PH increase.

The solution is to lower the TA until the CO2 outgasing rate goes down to close to zero. For most pools that happens when TA is around 60 to 70, though it varies from pool to pool.

 

[linen]

Just to add to what Jason said, the swg does not really produce NaOH. See:http://www.troublefreepool.com/for-waterbear-re-acid-usage-t174.html#p1139

 

[chem geek]

There is also the possibility of some chlorine gas not getting fully dissolved and outgassing instead. That would also cause the pH to rise and would not be helped by a lower TA level.

 

[POOLGOON]

Ok so the net rise in pH is basically neutral when the chlorine gets used up, however, i would assume that nobody lets all of their chlorine get used up before they add the next dose. So with this constant supply of chlorine coming from the SWG, wouldn't we see a consistently higher pH because of it?

And I don't fully understand why NaOH is not produced...

 

[JasonLion]

When you first turn the system on, and FC goes from 0 to say 4, there will be a slight PH increase. From then on, chlorine gets added and chlorine gets used up and as long as the FC level remains essentially constant the two cancel each other out and you won't see subsequent PH changes due directly to the SWG (except for the very usual case of chlorine outgassing, which almost never happens enough to measure).

Na is not involved in the process inside the SWG. The Na ions remain ions and do not combine with OH ions while in solution. You can see the complete chemical equations about half way down this post, look for the "Salt (SWG) Pool" heading.

 

[POOLGOON]

Alright i see what you mean now, thanks for putting it into perspective.
I's sorry these random questions keep popping into my head and you guys are the ONLY ones who can answer them correctly.