Water chemistry question

[ampsman]

So I am just getting started with figuring out my water chemistry and how to adjust it, so go easy on me.
I got my water report from Ward and was entering all the values in bru'n water. My water report includes Bicarbonate (HCO3) of 118. I also noticed that the spreadsheet has a calculator for Bicarbonate based on Total Alkalinity (CaCO3), which my report also included. So I plugged that in (150) along with the PH of 7.9 from my report and it gave me an estimated Bicarbonate concentration of 181.7. This is way higher than what my report actually shows. I assume I should go off the actual findings on the report but am curious the spreadsheet calculation is so far off.

 

[jerbrew]

This is from sheet 1 of Bru'N water (instructions):

If the calculated Alkalinity value does not agree with the Alkalinity presented in the Water Report, adjust the Bicarbonate content on the Water Report Input sheet to better match the reported value. If the calculated Permanent Hardness value does not agree with the reported Permanent Hardness, it may indicate that the the chloride or sulfate content is incorrect.