Managing pH and Total Alkalinity - Further Reading

Maintaining pH within a certain range is important because it can effect plaster, liners, equipment. Total Alkalinity has NO direct effects on the pool. Only through its effect on pH and CSI do we care about TA.

Except in a limited number of situations, TA and pH generally move in tandem. If you increase TA, pH generally increases. If you lower TA, pH generally decreases. This article discusses the relationship between TA and pH, and how to manage the two.

The primary purposes for looking at the Total Alkalinity and pH relationship are:
  • Knowing how to manage Total Alkalinity and pH together, because they typically move together, and
  • Total Alkalinity, pH, and their levels and relationship, are the number one cause of rising pH/Acid demand.

Adjusting pH may impact Alkalinity

In the relationship between Total Alkalinity and pH, pH should be your focus. Keep it between 7.0 and 8.0. Let Total Alkalinity be what it may. If you are constantly and frequently adding Acid, then Lower Total Alkalinity. Otherwise, manage pH an ignore TA.
Raising pH
pH rises naturally, and pH will rise without adding any chemicals. pH rarely has to be raised unless you added too much acid in lowering the pH or are following the process to lower Total Alkalinity. pH between 7.0 and 8.0 are fine, and do not need to be raised.
pH is raised the same way that you increase Total Alkalinity. If you find your pH is below 7.0, the best way to raise pH is through aeration. Aerations will increase pH without affecting TA. Borax is the next best solution, as it will raise pH, and have a small impact on TA. Soda Ash/Washing Soda is the next best solution. It will raise pH, and increase TA about 2 times the amount that Borax impacts TA. If you find you need to increase pH, and you don't have a way to use Aeration, use Pool Math to help you figure out how much Borax or Soda Ash/Washing soda to add. Baking soda is NOT a good choice to raise your pH. If your pH is below 7.0, then here is the general guidance.
If TA is 50 or above, bring your pH up to 7.4 or so using 20 mule team Borax.
If TA is below 50, then bring the TA up to 50-60 using baking soda and THEN raise your pH to around 7.4 using 20 Mule Team Borax.
Lowering pH
pH does not lower naturally. pH only lowers from additions of Acid. If your pH is dropping then acid is being added to the pool from some outside source, and is rare. Chlorinating tablets can have dry acid in them and will lower your pH and TA. pH is lowered in the same manner as lowering Total Alkalinity. If your pH is above 8.0, you should lower your pH.
Use Pool Math to determine, given the type of Muriatic Acid you are using, how much Acid to add. It will have a small effect on TA.

Adjusting Alkalinity will affect pH.

Total Alkalinity will not change if there are no external factors. Total Alkalinity will rise with the addition of high TA fill water or chemicals. Total Alkalinity will lower with the addition of acid or low TA water. As a general rule, you should NOT force your TA to a specific value or try and maintain a specific value. As long as TA is above 50, let it find its equilibrium with pH
Raising Total Alkalinity
The Alkalinity of pool water is raised several ways, primarily through the addition of an Alkaline agent. Depending on what you use, it will have varying effects on pH. This table shows the how pH changes when you raise TA by 10 ppm.
Baking soda has a small impact on pH and is the preferred method to increasing TA. If you have a need to raise your TA, and decide to use Washing Soda or Borax, understand it will raise your pH somewhat significantly.
Lowering Total Alkalinity
The Alkalinity of pool water is lowered using Acid. Adding Muriatic acid is the best way to reduce your TA, because alternative acids add other chemicals to your pool, or have other negative impacts on you or your pool. Dry acid should not be used in plaster pools or pools with a SWG. Adding acid lowers your TA, but it also lowers pH. This table shows the effect on pH by lowering TA by 10 ppm.

The higher the TA the more rapid the pH will rise over time.

Chemical TA decrease Associated pH decrease
31.45% (20 Degree Be) Muriatic acid 10 ppm .6 decrease
This is a significant impact on pH! Assume your 5000-gallon pool has a TA level of 120. You look up the recommended levels for your pool, and determine that your pool should have a TA of 80. If you add .4 Gallons of 31.45% of Muriatic acid to reduce your TA by 40, you will CRASH your pH by an astounding 2.5. Lowering TA should be done in stages described here Lower Your TA.

Can I change one without affecting the other?

Can I raise pH without affecting TA?
Yes, Aeration
Can I lower pH without affecting TA?
You cannot directly lower pH without lowering TA, as Acid (used to lower pH) also lowers TA. You can, however, reduce pH with acid, then add baking soda to raise TA back to the same level TA level where you started. This chart shows how to lower pH by .5 with acid and use Baking soda to restore TA. (amounts will vary by pool, use Pool Math to determine the correct amounts!)
Chemical/Action pH decrease Associated TA change
31.45% (20 Degree Be) Muriatic acid .5 8 ppm Decrease
Baking Soda 0 8 ppm Increase
Can I raise Total Alkalinity without affecting pH?
Practically? Yes, use Baking soda. You can add up to about 20 ppm of TA using baking soda while changing pH <.1. Larger additions of baking soda will have at least a .1 increase in pH. As an example, 80 ppm TA addition of baking soda would raise pH .2. If you have a need to raise TA more than ~20ppm, add 20 ppm baking soda, allow it a period of time to circulate, correct pH if necessary, then add additional doses (<20ppm) and adjust pH, until you hit your target TA.
Can I lower Total Alkalinity without affecting pH?
No and Yes. You will end up with the same pH, but lower TA if you use this process: Lower your TA. However, you will change pH many times while you are lowering TA.

Causes, and reducing pH rise

Causes of rising pH
The level of aqueous (dissolved) CO2 in pool water determines how fast pH will rise. Many pool owners experience constant acid demand and pH rises quickly, requiring constant additions of acid. There are several causes of high levels of CO2, rising pH and acid demand:
  1. Water features and aeration release CO2
  2. Lower pH water has higher levels of CO2
  3. Higher levels of TA allow higher levels of CO2
  4. When pool water has low pH and high TA, it has the most amount of stored CO2
For a deeper dive into the chemistry, start here: pH TA relationship - The Deep End
Reducing pH rise and acid demand
Turn off Water Features
Water features and aeration cause the release of CO2, which raises pH. The ways to combat this are to turn off the aeration or limit the time that one runs the water feature.
Cover your pool
A solar cover will drastically reduce the release of CO2.
Reduce your Total Alkalinity level
Practically, as pH rises, the rate of rise will slow. If the pH rise is faster than you care to maintain, reduce your TA until the rate of rise is reasonable to manage. There will become a point where the TA is sufficiently low, and your pH will slow to a reasonable level.
A reasonable starting point for most pools is a TA of 80-100. Most find, however, particularly with SWCG pools, that a TA of 60-80 slows their pH rise sufficiently, hence the TFP recommended levels. TA can be safely lowered as far as 50 ppm if necessary. The TA range in the Recommended Levels is designed to protect your pool surface as long as the pH, TA, and CH can be kept in recommended ranges.
The scope of this article is to help you better manage Total Alkalinity and pH together. It will not get you to a permanent, zero acid demand pool. It will significantly extend the period between acid additions.

Other Questions

If TA in the water contributes to pH rise, can I just get rid of all the TA?
TA levels below about 50 ppm lead to insufficient levels of TA to buffer pH to prevent sudden pH crashes.
Can I ignore my Total Alkalinity lever if my pH is steady?
No and Yes. No because you should perform regular testing to ensure TA doesn't go below 50. Yes because you now understand the relationship between TA and pH, and that one of the primary objective of TFP is to have a pool that has reasonable rising pH levels and acid demand. Once your pH rise is manageable, you have met the objective. Your pool is in reasonable equilibrium. Sit back and enjoy!