Experts: TA levels--SWGs

[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.

 

[Stoopalini]

Anode 4Cl -> 2Cl2.
Cathode 4H2O -> 2H2 + 4OH.
2Cl2 +2H2O -> 3H + HOCl + OCl.
HOCl + OCl + uv light -> O2 + 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.

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

Here is a thread Richard created a while back, where he was trying to understand where the pH rise is coming from. I thought it was universally understood that a SWCG does result in a pH rise ... some more than others though?

pH Rise in SWG Pools

I was involved in an unfortunately not-so-nice exchange in this thread, but the net result is that I calculated the volume of hydrogen gas bubble production in an SWG and found that even under best-case conditions with perfect kinetics, there simply isn't enough volume of gas generated to remove...

www.troublefreepool.com

Here's a quote from his intro:

I was involved in an unfortunately not-so-nice exchange in this thread, but the net result is that I calculated the volume of hydrogen gas bubble production in an SWG and found that even under best-case conditions with perfect kinetics, there simply isn't enough volume of gas generated to remove carbon dioxide (at equilibrium quantities using Henry's Law) at a rate to explain the significant pH rise in SWG pools. Though lowering the TA will reduce the effect of pH rise from carbon dioxide outgassing, in many SWG pools this doesn't help enough and my theory of hydrogen gas bubbles increasing aeration cannot be the primary source of pH rise.

So I looked for other reasons and the most likely candidate is that of chlorine gas outgassing since that is also produced in the SWG and if not fully dissolved into the water it can outgas (once it becomes aqueous chlorine then this combines with water to form hypochlorous acid very quickly and does not outgas very much). This means that there may be other methods that can help slow down the rate of pH rise in SWG pools. For example, pointing the returns downwards may help make the chlorine gas bubbles spend more time in the water and therefore dissolve more completely so less gets outgassed. Using a slower pump speed can help the chlorine spend more time in the pipe, at least in larger pipe and longer pipe runs.

 

[JamesW]

My observation is that SWGs cause zero pH rise.

In my opinion, it's just not something that happens.

pH rise comes from carbon dioxide offgassing.

The only thing that changes is that you lose about 0.25 lb of water for every pound of chlorine gas generated.

This is due to the water being converted into hydrogen gas and oxygen gas.

 

[JoyfulNoise]

My pH rise is entirely the result of having fill water with a TA of 110ppm being added daily to compensate for evaporation. When my TA is held down to 50-60ppm, there’s almost no pH increase I can detect. How do I know this? In the winter my fill water usage goes down to next to nothing as the water cools. I can go weeks without adding any acid and the TA stays right where I leave it. During that time my SWG will still run because I haven’t hit the cold water cut off temp yet. There is no pH rise.

People that live in areas with acidic, low TA fill water (typically East And South of the Mississippi ) will also report that SWGs don’t cause pH increases (they also tend to have vinyl liner pools). In fact, I remember one pool owner on TFP that had to regularly add soda ash to the pool to keep the pH up otherwise their pH would drop to far.

 

[Saturn94]

My pH rise is entirely the result of having fill water with a TA of 110ppm being added daily to compensate for evaporation. When my TA is held down to 50-60ppm, there’s almost no pH increase I can detect. How do I know this? In the winter my fill water usage goes down to next to nothing as the water cools. I can go weeks without adding any acid and the TA stays right where I leave it. During that time my SWG will still run because I haven’t hit the cold water cut off temp yet. There is no pH rise.

People that live in areas with acidic, low TA fill water (typically East And South of the Mississippi ) will also report that SWGs don’t cause pH increases (they also tend to have vinyl liner pools). In fact, I remember one pool owner on TFP that had to regularly add soda ash to the pool to keep the pH up otherwise their pH would drop to far.

I‘m one if those in the SE that doesn’t experience pH rise running the SWCG (TA around 70). It use to rise back in the day before I knew any better and kept TA at 100+.

I haven’t used MA or baking soda in years.