PoolMath Inaccuracy

[revitup]

Am I the only one confused about the resulting tested levels following chem additions, relative to the predicted PoolMath results? The differences seem to me to be beyond any reasonable margin of error. I could not be sure in the past that the errors were not the result of my 'guestimate' of my pool volume but I just completed a complete water exchange, noting my water meter readings, and now know exactly what my actual pool volume is (8500 gal).
Examples, after sweeping thoroughly to mix and waiting 24 hours to retest:
SALT:
Initial test result: 400.
Addition: 80 lbs
Subsequent test result: 1200
Pool Math prediction: 1525 (400 + 1125 from PoolMath 'Effects Of Adding')
TA:
Initial test result: 20.
Addition (baking soda): 32 oz
Subsequent test result: 50
Pool Math prediction: 37 (20 + 17 from PoolMath 'Effects Of Adding')
Is it unreasonable to expect better than up to 35% error in predicted values?

 

[JohnT]

Am I the only one confused about the resulting tested levels following chem additions, relative to the predicted PoolMath results? The differences seem to me to be beyond any reasonable margin of error. I could not be sure in the past that the errors were not the result of my 'guestimate' of my pool volume but I just completed a complete water exchange, noting my water meter readings, and now know exactly what my actual pool volume is (8500 gal).
Examples, after sweeping thoroughly to mix and waiting 24 hours to retest:
SALT:
Initial test result: 400.
Addition: 80 lbs
Subsequent test result: 1200
Pool Math prediction: 1525 (400 + 1125 from PoolMath 'Effects Of Adding')
TA:
Initial test result: 20.
Addition (baking soda): 32 oz
Subsequent test result: 50
Pool Math prediction: 37 (20 + 17 from PoolMath 'Effects Of Adding')
Is it unreasonable to expect better than up to 35% error in predicted values?

 

[JohnT]

Not sure what is going on, but I did the first two manually and with Pool Math and the PM answers are correct.

 

[mknauss]

For salt testing, we can assume you are using a K1766?
For TA testing, you used your K2006C with a 25 ml sample for 10 ppm accuracy?

 

[MiguelACA]

Am I the only one confused about the resulting tested levels following chem additions, relative to the predicted PoolMath results? The differences seem to me to be beyond any reasonable margin of error. I could not be sure in the past that the errors were not the result of my 'guestimate' of my pool volume but I just completed a complete water exchange, noting my water meter readings, and now know exactly what my actual pool volume is (8500 gal).
Examples, after sweeping thoroughly to mix and waiting 24 hours to retest:
SALT:
Initial test result: 400.
Addition: 80 lbs
Subsequent test result: 1200
Pool Math prediction: 1525 (400 + 1125 from PoolMath 'Effects Of Adding')
TA:
Initial test result: 20.
Addition (baking soda): 32 oz
Subsequent test result: 50
Pool Math prediction: 37 (20 + 17 from PoolMath 'Effects Of Adding')
Is it unreasonable to expect better than up to 35% error in predicted values?

I have noticed this with my pool math app. I should expect a certain change after following the recommended dosage from pool math, but I typically get a lower thane expected result. I have my pool math app set to 5000 gallon pool when in reality its closer to 5500 gallons. I haven't sat down to math it all as pool math numbers get me close enough...could it be you have the gallons wrong?

 

[MiguelACA]

I have noticed this with my pool math app. I should expect a certain change after following the recommended dosage from pool math, but I typically get a lower thane expected result. I have my pool math app set to 5000 gallon pool when in reality its closer to 5500 gallons. I haven't sat down to math it all as pool math numbers get me close enough...could it be you have the gallons wrong?

So i noticed you recently did an exchange and tracked the water sued to fill.

One other thing I have noticed is if on the dashboard, i select a variable that is off (Too high or too low) , the amount it tells me to add does not typically show the same number as if i went to the "effects of adding" tab.

for example, my currency ph is 7.6 and ta is 80. the ph tab says to add 15oz of 31.45% acid to lower it to 7.0. If i go to "Effects of adding" and i plug in 15oz of 31.45% acid, it shows it will drop ph 0.7. Its not a huge difference, but i have noticed the discrepancy between "Effects of adding" and the amounts/effects in the actual chemical tab.

 

[mknauss]

Read the fine print, especially for pH.

 

[revitup]

For salt testing, we can assume you are using a K1766?
For TA testing, you used your K2006C with a 25 ml sample for 10 ppm accuracy?

Yes and yes.
Ran both tests more than once, same results.

 

[MiguelACA]

Read the fine print, especially for pH.

I read it after I posted...my bad, forgot to come back and respond

 

[revitup]

I adjusted salt again yesterday and once again the results do not match the Pool Math prediction.
After sweeping thoroughly to mix and waiting 24 hours to retest:
SALT:
Initial test result: 1200
Addition: 49 lbs
Subsequent test result: 2200
Pool Math prediction: 1889 (1200 + 689, effect of 49lbs from PoolMath)
Given that each drop in the salt test is 200, I could see an error of +/- 100 but an error >300 ppm? Seems excessive but maybe my expectations are too high.