alkalinity confusion

[rhthompson]

Many sources say that baking soda acts as a "buffer" to prevent pH swings, but i just don't get it. It seems to me that baking soda is more just a "neutralizer" to acid. To try to raise TA i add baking soda, and the pH goes too high, so i add muriatic acid to bring the pH back down, but it also brings TA back down. Seems like a vicious cycle. Can anyone help me make sense of this? Thanks. PS: i took chemistry in school.

 

[mknauss]

Alkalinity is the buffer for the pH.

Can you post a full set of test results?

 

[rhthompson]

Alkalinity is the buffer for the pH.

Can you post a full set of test results?

thank you for replying.

28000 gallon gunite pool, replastered 2 years ago.

test results
Alkalinity a week ago was 50 ppm, today is 70 after having added 8 lbs baking soda over the last few days.
pH after adding a pint of muriatic this morning is 7.7; based on past experience it will be back up to 7.8 by tomorrow
Chlorine 2 ppm (i add bleach in the evening for Cl)
Calcium 300 ppm
CYA 33 ppm
metals, nitrates, phosphates, dissolved solids all 0

I have added several boxes of baking soda over the months to increase TA but pH always creeps up, so i add muriatic and that brings the TA back down. Taylor "Pool & Spa Water Treatment" booklet says 3.2 quarts of muriatic will decrease alkalinity in 20K gallon pool by 20 ppm, so at the rate i usually need to add muriatic i would be back down to 50 ppm TA within a few weeks unless i keep adding baking soda.

So is the answer to just keep pitting baking soda and muriatic against each other?

 

[mknauss]

I take it from your test results those are from a pool store.

Do you have your own test kit?

No reason to adjust pH until it reaches 8. Only lower it to 7.6.

Do you have any water features running most of the time?

 

[rhthompson]

I take it from your test results those are from a pool store.

Do you have your own test kit?

No reason to adjust pH until it reaches 8. Only lower it to 7.6.

Do you have any water features running most of the time?

test results for TA, pH, and Cl are from my Taylor kit and a Home Depot kit, other results are from pool store.

only thing that might count as a water feature is a small fountain that comes up from telescoping tube in the bottom of the pool -- produces a stream a foot or so above water level. Runs 24/7 but at low pump speed 2/3 of the time

thanks

 

[mknauss]

Stop that and your ph rise will lessen.

I suggest you get your own proper test kit.

 

[JohnT]

Many sources say that baking soda acts as a "buffer" to prevent pH swings, but i just don't get it. It seems to me that baking soda is more just a "neutralizer" to acid. To try to raise TA i add baking soda, and the pH goes too high, so i add muriatic acid to bring the pH back down, but it also brings TA back down. Seems like a vicious cycle. Can anyone help me make sense of this? Thanks. PS: i took chemistry in school.

It is a buffer. It’s a bit complex, but it’s the same thing that happens in natural bodies of water and even your blood. Google carbonate buffer system for an explanation if you want details.