Alkinity & ph relationship

[CesarZambrano]

Hello I was wondering what the relationship was like with alkinity and PH in spas as I know that they get so much aeration you want your alkinity to be around 30-40ppm. Or at least that whatr has worked for me considering I have a 1,000 Gallon spa. Although what I am confused about is something I have encountered today where my co-worker showed me that his spa (of the exact same size) had his PH at around a 8.0ppm and we checked his alkinity to see what what us up and it was the same deal as mine, at a 30ppm?

If both our spas are the same size and his alkinity is at the same level as mine why is my PH performing so much better (7.4ppm) than his?
I am wondering if we should raise or lower his alkinity to stabilize his PH but that's just where I'm confused. His ALK is already at 30ppm, pretty low if you ask me, and if we lower it even more should that do the trick??

 

[zea3]

Are y'all using the exact same chemicals in the same amount? Do you run your spas the same amount of time with the same injection volume and rate of air? Do you both leave the spa covered/uncovered when not in use? What I am saying is many factors influence pH rise, and it is virtually impossible for you both to have the exact same factors in two separate spas. If your friend's spa likes to sit at 8.0 and he is comfortable with that level of pH then nothing needs to change. I would not try to lower his TA if the pH is stable.

 

[DangerBoy]

You should take a look at this article. The first part explains about the relationship between pH and TA. https://www.troublefreepool.com/threads/9670-How-do-I-use-Chlorine-in-my-Spa-(or-pool).

Basically, TA is a measure of the water's ability to absorb acid. Generally, it's related to the concentration of the bicarbonate ion in the water. According to the TFP method, you want your TA to be around 50 in order to get your pH to be relatively stable. If your TA is higher than that you're supposed to drop the pH to about 7.0 - 7.2 and aerate until the pH comes back up to about 7.8 and keep doing that until you hit your target TA level. What's happening there is that by dropping the pH and aerating, you're getting rid of the bicarbonate ions by converting them to CO2 which off-gasses through the aeration. Some hydroxyl (OH+) ions are created in the reaction so the pH rises as the CO2 off-gasses.

If you guys are both sitting at about 30 ppm for TA, you might want to try raising it to 50 by adding Calcium Chloride which around here is available cheaply in the form of sidewalk/driveway de-icer. Then adjust your pH with either acid or baking soda depending on where your pH ends up at the end of the TA adjustment process. You can add some additional buffering ability to your water to help keep your pH a little more stable by adding 40 ppm borate. You can do that by either adding boric acide or borax and some acid.