Difference between "Effects of adding" and calculated addition from test results

[Sam721]

Hi everybody,

I am using PoolMath to figure out how much MA to add to lower pH and I am getting inconsistent results.

So I measured pH and it was 8.0, and I wanted to lower it to the bottom end of the ideal range, so 7.6. That screen is telling me to add 26oz to basically lower pH by 0.4. But when I go to "Effects of adding", and put in 26 oz, it tells me it will lower pH by only 0.2? It doesn't allow you to input the current TA to calculate how much to add on that screen however, but I am within the range listed at the bottom. What's going on here? Which number to trust? Isn't the same math behind both these screens?

Measuring pH again after adding the suggested MA amount tells me that I am somewhere in the middle between a 0.4 and 0.2 pH change, but I am wondering what's different in the calcs being done for both these screens.

Thanks!
Sam

 

[PoolStored]

Look at the warning note in the Effects section. It clearly says that the pH calculations are approximate because it has to make certain assumptions about other values in order to do the calculations. PH is impacted by many factors, TA, borates, etc. The more info entered into Poolmath the more accurate the calculation, which the calculated addition has and uses...the "effects of adding" if I'm not mistaken does not use your pool math logs, only what is input on the screen.

 

[Sam721]

Thanks for replying. I did read that note, and that's exactly where my question comes from: what does the left screen (suggested addition) do different than the right screen (effects of adding)? Is it just the TA? I tried changing the TA input but even extreme inputs never came close to cutting that pH change in half...

 

[PoolStored]

what does the left screen (suggested addition) do different than the right screen

All the last chemical test logs in your pool math for that pool.