Pool Math calculations

lawjohn

Well-known member
May 2, 2013
62
I hope someone knows this answer....An example: suppose your pH is 7.8 and your TA is 70. Now you want to lower your pH to 7.4 and raise your TA to 90. Does the Pool Math calculation for each (pH and TA) take in account the other one in recommending how much chemical to lower the pH and raise the TA. Hope this question is clear. Thanks lawjohn
 

Donldson

TFP Expert
LifeTime Supporter
Jun 12, 2009
4,585
NW Ohio
AFAIK, no. The calculations are separate.

Why would you want to do that anyway? You're basically just doing offsetting adjustments and within a day you'll be right back where you started.
 

lawjohn

Well-known member
May 2, 2013
62
The reason for the question is that TA is raised or lowered linearly and pH is raised or lowered logarithmic. The pool math says on the TA that raising the TA will slightly raise the pH.....therefore the question on how the calculations in my question is accounted for or not at all.
 

lawjohn

Well-known member
May 2, 2013
62
Forgot to mention in my reply post that I'm trying to understand how the calculations take in account the other recommendations given. I know what the target numbers are to keep my pool within the target numbers..... it's a question of how the Pool Math calculator was designed to provide the recommendations it gives...lawjohn
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,284
Tucson, AZ
The calculations are separate.

Calculating TA is fairly simple because it's just simple accounting of the mass of solute added to the water. So if you add XX amount of a chemical that raises some part of the TA (carbonates, borates, hydroxides, cyanurates, etc), then that increases the TA by YY ppm. Adding acid lowers the TA because it adds hydrogen ions (H+) particularly if it is a strong mineral acid like muriatic acid. There's a little bit of equilibrium chemistry for certain types of chemicals, but that's still nothing more than a little bit of accounting.

If you're not a chemist then you're not as familiar with the concept, but suffice it to say that pH calculations can get quite complex even for the simplest acid-base-buffer systems. Because pool water is a mixture of various buffers (carbonates, cyanurates and, possibly, borates), there is no closed-form mathematical solution for how adding acid or base changes pH when all three buffers are present. It's actually about a dozen or so equations that need to be solved simultaneously for any given set of initial conditions....it's a calculation process that is well beyond the scope of any website programming or app programming.

So how does TFP calculate pH?? It does it just like all the other pH reference guides (like the charts in the Taylor booklet), the programming makes a large number of assumptions about the pool water and then uses a linear interpolation of a known set of data points to create an output value. The upside is that it's easy to code, the downside is that the calculation is really only accurate over very small pH changes. If you're trying to adjust your pH by more than +/- 0.2 units, the calculated additions are a very rough estimate at best.
 
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JamesW

TFP Expert
Mar 2, 2011
20,783
suppose your pH is 7.8 and your TA is 70. Now you want to lower your pH to 7.4 and raise your TA to 90.
There's virtually no case where that would be a desirable thing. If the pH is going too high, the TA is usually too high. If the pH is going too low, the TA is too low. When the pH stays at the correct level, the TA is usually right.

There are a few cases where you might want to do both at the same time, but it's very rare.