SWG run time and PH creep - any science to support this?

[JonoVegas]

I have noticed this year (here in Vegas) that might PH is much more stable so far than in previous years. All variables are pretty much the same except I am running my SWG for much shorter time periods at a small bump in "% on rate".

I almost hesitate to even tempt the pool gods since things are great right now, but is there any basis for a shorter SWG run cycle having less impact on PH rise? Hopefully not just an early season phenomenon.

 

[PoolGate]

What is your TA?

 

[mknauss]

SWCG use has little effect on pH in pool water.

The biggest push on pH in our area is the TA of the fill water. If you are adding less fill water, your pH will rise more slowly.

 

[JonoVegas]

Probably adding less pool water so far, well into June, due to lower than normal temps here in Vegas. Most logical explanation is the likely low auto fill so far.

Chems:
FC: 6
PH: 7.7 and extremely stable so far
TA: 100 and extremely stable so far
Water temp: 86.3
CH: 450
CYA: low, probably around 40 but I gave up measuring this cause my FC has been pretty easy to control with my SWG
Pool cover: on always when not swimming
SWG running 3.5 hrs @ 60%
Pool pump running low speeds about 15 hrs / day at low speed

 

[JoyfulNoise]

If LV's weather has been as weird as Tucson's weather, then that is also playing a part. Our overnight temps are still dipping into the 60's and my pool is starting off every day at < 78ºF. Temperature has huge impact on FC demand. Once my pool starts getting above 85ºF , I notice my FC consumption goes up. Every 10ºF rise in temperature will double the reaction rates for chlorine consumption. It also affects the outgassing rate of CO2 which will determine the pH rise.

So if your pool is staying a little cooler than normal, that could be it too.

 

[mknauss]

Pool cover: on always when not swimming

That make the pH stable or fall. And dramatically reduces evaporation. I doubt you will have that on the pool once it warms up.

 

[jmastron]

In my pool, there IS a noticeable difference in pH rise rates (days between reaching 8.0 and adding in my case) correlated with adding more vs less chlorine (i.e. when the cover is on, or the temps are low/sun is less), BUT I didn't notice a difference in that behavior when I installed the SWCG vs when using liquid chlorine before.

It may not be adding chlorine that directly causes a pH rise, but rather the conditions that are causing FC to be used more vs less (and thus causing us to adjust SWCG times or add more)?

I think the reports get mixed up a bit because people switching from trichlor tabs to SWCGs will see a big difference in behavior, as the trichlor is naturally acidic. There it's not that the SWCG (or liquid chlorine) is causing the pH rise, it's that previously they were adding acid via the tabs keeping it down. Those using liquid chlorine before most likely already were adding muriatic acid on occasion, and I wonder how many of us saw a difference when switching to SWCG; I suspect a lot less.

 

[tfpflana1502]

Probably adding less pool water so far, well into June, due to lower than normal temps here in Vegas. Most logical explanation is the likely low auto fill so far.

Chems:
FC: 6
PH: 7.7 and extremely stable so far
TA: 100 and extremely stable so far
Water temp: 86.3
CH: 450
CYA: low, probably around 40 but I gave up measuring this cause my FC has been pretty easy to control with my SWG
Pool cover: on always when not swimming
SWG running 3.5 hrs @ 60%
Pool pump running low speeds about 15 hrs / day at low speed

May I ask how you know your SWG is running for 3.5 hours? Also, with all things being equal, did you gradually get to 60% salt generation, or did it creep over a couple years? I've had my T-15 for 2.5 years now and just hit 35% for the first time ever where usually it runs at 20%. CYA is a big factor.