Baking Soda - Ta And Ph

[pskkd930]

I must be missing something. From everything I've read, Baking soda should increase the PH slightly and the TA significantly. The last couple of times I've added Baking Soda, my PH has shot way up.

This morning my PH was at 7.2 and TA was at 60. I added 2 oz of Baking Soda and checked 2 hours later. The PH was at 7.8 and the TA was at 130. I use a Taylor kit for testing.

What am I missing? Do I need to wait a full 24 hours to test again? I did run the jets for a few minutes and the circ pump ran for at least one of those hours.

Thanks!

[waterbear]

With a TA of 130 there will be significant ougassing of CO2, particularly with the jets running and outgassing of CO2 from aration of the water is the primary cause of pH rise. Depending on your choice of sanitizer a pH of 7.2 and a TA of 60 might have been perfect. Howver a TA of 130 is a bit high,IMHO. a pH of 7.8 is high end of acceptable for chlorine or silver/mps and well within range for bromine.

[pskkd930]

Thanks waterbear! I agree it's a little high. I used the Pool calculator referenced in Nitro's post and it said the baking soda of 2 oz should only make an increase of roughly .1 PH and 40 TA or so.

Should baking soda be making that kind of a PH jump? I'm using the dichlor bleach method

[chem geek]

If you add baking soda quickly so it is concentrated on the surface of the water, you may notice some bubbling. If that happens, then that's carbon dioxide outgassing from the locally high TA. So this is one of the unusual times when how you add the chemical can affect the result. The TA always rises by the amount of baking soda you add, but the pH may rise more than indicated by the calculator if there is carbon dioxide outgassing that occurs. Having a higher TA level and having aeration accelerate such outgassing.

If you are using the Dichlor-then-bleach method, then why are you raising the TA? You should generally keep it low at around 50 ppm or so to minimize the pH rise from carbon dioxide outgassing.

By the way, what volume is your spa? 2 ounces volume of baking soda in 350 gallons raises the TA by 32 ppm (though depends on the density of the baking soda and how you measured it, whether you tapped it down, etc.). 2 ounces weight of baking soda in 350 gallons raises the TA by 26 ppm. So where did you get The Pool Calculator to give you 40 ppm? The fact that you measured a much larger TA rise would seem to indicate that either 1) you didn't wait for it to circulate before measuring it or 2) your measuring was wrong and you added more than you think.

[pskkd930]

Thanks Chemgeek, I really appreciate taking the time to point me in the right direction.

To answer your questions, the hot tub is 420 gallons and honestly the reason I added Baking soda was because the PH was low and I had some readily available. The last time I added baking soda I also saw the PH rise so this was kind of a scientific experiment. You are correct that it should have only increased the TA by 20(I transferred that wrong) which is why I'm so confused. I weighed it out using a scale and perhaps that's what I need to look further into. Sounds like my scale may be crazy inaccurate.

[Spanky]

I've found, in my limited experience, that raising the pH of a hot tub requires a bit of careful thought. You have to look at the TA before you decide what action to take. Other than addition of acid, I've found that there are basically 2 scenarios that result in low pH. The first is inactivity, where the net acidity of the sanitizer has not been counteracted by outgassing of normal aeration (vacation for example). In this case the TA will usually be somewhat normal (above 50ppm) The solution, as stated in the above posts, is simply to aerate. The second scenareo is when the TA drops too far (usually below 40ppm). In this case simply add enough Baking Soda to raise the TA Back to 60, or whatever you find is normal for your spa, then areate.

50ppm Borates also helps keep pH in balance

I've honestly never found any need for such things as pH up (Washing Soda). If your TA is high, the pH will usually tend to rise. In that case (above 7.8) carefully add acid then aerate to restore pH and lower TA. The "trick" is to allow the tub to find it's own equilibrium. Once you find it you'll find that the tub will stay there for several weeks, if not longer.

For me this seems to happen @ TA: 50ppm, pH: 7.6 and 50ppm Borates.