Something's wrong in the calculator


Apr 9, 2009
Tested pool this morning. Findings:
Pool size 15300 gallons
FC – 6
PH – 8.2
TA – 140
CH – 190
CYA – 50
Borate – 45
Salt – 3600
Temp – 81

Trying to drop PH down to 7.4. Using Web based pool calculator it calls for 115 oz. of 31% Muriatic Acid. Checking effects show lowering of PH by 1.81.
To verify I went to the app, on iPhone, and it calls for 29 oz of Muriatic Acid.
Something is wrong. What is correct?

And yes I know I need to kick the CYA up some more. Doing it slowly.


TFP Expert
Platinum Supporter
May 23, 2015
Tucson, AZ
You should never use any pH calculator to make adjustments that large. All of TFP’s tools clearly state that any pH adjustment greater than 0.2 units will be inaccurate or, at best, rough estimates. pH calculations in a multi-buffered solution (there are three strong buffers in your pool water) is a highly complicated and complex calculation to make. No web tool can do it accurately.

I suggest you make smaller, incremental adjustments to pH so that you don’t damage anything.


Apr 9, 2009
I started out with 29 oz's to see what happens. I never add all that's needed at one time.
I reentered the data into the app and still comes back 29 fl oz.
I just think it was strange that the app and the calculator didn't agree. Not even close.