Stable Ph with SWCG....is this normal?

[JimK]

Quick background (see pool specs in sig): I have always used SWCG since pool was installed in 2004. Up until this season, I've always had to add a weekly dose of muriatic acid to keep the Ph "in range"; ie 7.4-7.6. I understand with a SWCG it's normal for the Ph to rise over time.

This season I remember reading somewhere in this forum to not worry about lowering Ph until it rises above 7.8 (previously I would lower it once it hit about 7.6). Well, once Ph rose to about 7.6-7.7 it stopped rising! It's been about 6 weeks since reaching that point and Ph has stayed absolutely stable!

Here's the latest numbers (using PF recommended Taylor kits):
Ph (or is it pH?) 7.6-7.7
FC 5.5
CC 0
TC 5.5
TA 100
CYA 80
Borates approx 60
Calcium Hardness 240
Salt 3100
SWCG set to 60%, pump on 14hrs a day during the daytime

I expected with the SWCG that Ph would continue to rise above 7.6/7.7 and I would have to lower it at some point, but this isn't happening.

Is this normal for a pool using a SWCG?

[AnnaK]

Ph (or is it pH?) 7.6-7.7

It's pH.

The 'p' can stand for a number of things: power, potency, decimal cologarithm of, potential. The 'H' stands for the hydrogen ion. The other day I saw the pH measurement shown in terms of ppm. pH is not expressed in units. It doesn't have any.

[chem geek]

As shown in this chart, the amount of over-carbonation of water with respect to air is less at higher pH (and lower TA) which is why the rate of rise in pH slows down as the pH gets higher especially when using borates since they buffer more strongly as the pH rises. Nevertheless, you usually see pH rise continuing when the TA is at 100 ppm -- you usually have to have it lower at 70 ppm or so for an SWCG. It all depends on the amount of aeration in your pool -- every pool is different. Just be thankful yours has become stable.

[waterbear]

with borate in the water the pH tends to stabilize at around 7.7 for a much longer time than without borates, SWCG or not. As chem geek said, dropping the TA down to around 70 ppm seems to be the 'sweet spot' for TA with borate and a SWCG.

[JimK]

Thanks for the feedback.

So will my TA go down over time or does it require action on my part to lower it? Since everything has been very stable I'm not inclined to tinker with it at this point and just enjoy it.

[waterbear]

The only thing that will cause TA to go down it adding acid. If your pH is staying stable enough for you now don't change it but as chem geek and I said before, most SWCGs seem to exhibit the BEST pH stability with the TA at around 70 ppm and 50 ppm borate (with CYA at the manufacturer's recommended maximum) and there is several years of evidence in actual pools to back this up from various forums and other sources.