Discrepancy in Pool Math?

[jesse-99]

I'm sure this is user error, but... if I'm in Pool Math and on the Home Page, and select the pH button on the top right, entering a target pH of 7.1 (from 7.9 with TA of 300), tells me to add 2.5 gallons of MA.



If on the other hand, I use the Effects of Adding page instead to figure out how much MA to bring my pH from 7.9 to 7.1 its basically 1 gallon as per this screenshot:



If I change Effects of Adding to 2.5 gallons , it says pH goes down by 2.2 (whereas the FIRST screenshot above says the -same- amount will only lower pH .8, not 2.2??

What am I missing here? Or is this some kind of calculation discrepancy in the app?

 

[mknauss]

Read the NOTE at the bottom of the Effect of Adding panel.

 

[kellyfair]

Check the settings for the pool in the first screenshot - make sure the size is correct.

 

[jesse-99]

Check the settings for the pool in the first screenshot - make sure the size is correct.

Yep the size is 35,500 in the first screenshot, just like it is in the Effects of Adding, also 35,500.

 

[kellyfair]

Is your total alkalinity really 300?

 

[jesse-99]

Read the NOTE at the bottom of the Effect of Adding panel.

I see that, and I think the accuracy of Effects of Adding is pretty accurate based on my before/after testing. The home page -> pH screen, loses some accuracy when you make large pH jumps (for example, 7.9 to 7.1). When you instead tell it 7.9 to 7.4, it's way more accurate at 1.25 gallons (which correlates well with my addition of 1 gallon this morning, which bring my pH down to 7.4, tested 1 hour after adding.

I'll be my careful about the math for large pH adjustments... (Just refilled pool, and TA is a fun 300 so working at bringing it down.)

Thanks for the tip.

 

[jesse-99]

Is your total alkalinity really 300?

Yep, it was 330 with the fill. from the other day. fun times... My well has been high TA forever.

 

[PoolStored]

Read the NOTE at the bottom of the Effect of Adding panel.

^^^^This...