PoolMath provides inconsistent muriatic acid results

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S

Sonosite

Member
Apr 23, 2021
8
Southlake, Texas
Pool Size
24500
Surface
Plaster
Chlorine
Liquid Chlorine
When trying to calculate how much muriatic acid to add to the pool based on pH difference from 7.9 to 7.6, PoolMath tells me to add 64 fluid oz of 31.45% MA.

However, when trying to cross check by verifying under the "effects of adding", PoolMath tells me that adding 64 fl oz of 31.45% MA results in pH drop of 0.6

Actual pH testing indicates that i actually drop the pH closer to 7.3

Why is there the inconsistent MA amount recommendation in PoolMath?
 

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From pool store result. When i test it, it's 90. I use the pool store as an adjunct to my own testing. I know TFP frowns against using a pool store, but i like to compare with my own testing and i also don't trust my CYA testing results yet
 
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Sonosite said:
Why is there the inconsistent MA amount recommendation in PoolMath?
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Because of this, from your second screenshot:

Screenshot_20220822-190535.jpg

"Effects of adding" is a simpler ballpark calculation that doesn't take TA into account. But I can't tell you why that calculation seems to match your actual result better than the TA-dependent calculation.
 
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👆 that, plus another thing: Not all "0.6" are the same. It takes different amounts of acid to reduce pH from say 8.2 to 7.6, than from 7.6 to 7.0. The pH scale is a logarithmic scale: pH = -log10([H+])

Same amounts of MA change the the H+ concentration by same amounts, but because you have to take the logarithm to get the pH from the H+ concentration, the pH-difference depends on the starting pH.

As Drew said, "Effects of Adding" is really only a ballpark number for pH. Any pH calculation that doesn't need the starting pH and the current TA as an input, can only be a rough estimation.

But the calculated TA change for a given MA addition is pretty good in the Effects of Adding.
 
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In addition to that, there’s a note saying that as the pH change increases, the estimate accuracy decreases. I think it’s anything below a 0.4ph change is reasonably accurate but more than that is not so much.
 

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Sonosite said:
This is a surprise. Any guess why your results in PoolMath are different than mine? I have the most updated version of PoolMath (on android device)
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Never mind. I figured it out. During the spring, I added borates and adjusted the borate level to 50. However, I stopped tracking it. High borate level means you need more MA to counteract. I don't think my borate level is truly at 50 ppm.
 

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Yep, that would explain it. There was a similar situation recently:

pH dropped MUCH lower than Pool Math predicted?

This is the 1st time this has happened to me in the 2 years I've been managing the pool. I've always done the TFP method, and it's been great! While my neighbors have pool service companies coming once (sometimes twice) a week, and they still experience algae blooms ... I've never had any...
www.troublefreepool.com www.troublefreepool.com

Especially explains the difference to effects of adding, as that doesn't consider Borates at all.

Just a bit surprised about PoolMath there, because it wasn't showing in your screenshot. Must be, because you have disabled tracking Borates, but it still seems to consider the Borates test result for the acid addition calculation without being able to adjust it.
 
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