Chalk (CoCO3) calculation off compared to other calculators

[Brewer #124535]

I noticed that adding 1 gram of Chalk to 8 gallons of distilled water added 6.6 mg/l of Ca and 20.137 of HCO. Other calculators, EZ Water Adjustment, and Brew Smith with the same amount of water and the same amount of chalk add 13 - 13.2 mg/l of Ca and 19 - 19.8 of HCO. The more Chalk that is added the larger the delta between calculations gets. For example, 10 grams of Chalk yields 66.1 Ca here, while the same amount yields 132 Ca on EZ Water and Brew Smith.

 

[oliver]

does this have to do with acidity and carbonation thing @Nosybear ? Is brewers friend accounting for something that the other calculators are not (or vice versa)?