Right, firstly that doesn’t show you need 48.8mg Sodium Bicarb, it shows you need 48.8mg/l Bicarbonate.
The table below that shows how much sodium bicarb (or another source of bicarbonates to add).
E.G The Molar mass of Sodium Bicarb = Molar mass of Sodum + Molar mass of Bicarbonate (1 of each)…..the molar masses are listed on the spreadsheet.
The amount of bicarbonate you want to add is = to the bicarbonate required for alkalinity. The amount of sodium you get will be automatically calculated to the right hand side of the table based on this.
Underneath you define whether or not you’re making a concentrate. Since you’re not you follow the instructions for that, from memory you change “the amount of concentrate to use” under “ml” to 1, “to be added to” to 0 the “amount of concentrate to make” to whatever quantity of water you are remineralising directly. This makes the dilution cell read “1” which is to say no dilution is taking place and you then define the quantity of water you’re dealing with….if you want to break the spreadsheet for future use you can just edit the red dilution cell to 1.
So the amount of Sodium bicarb you need to add is defined by the bicarbonate you need to add to get the alkalinity with the addition of the sodium you will also add by default to get that alkalinity.
Use the same process for whatever other source of Bicarb you might use and whatever source of hardness you use, as you’ve decided you want to add hardness. You have many sources of Mesgnesium to choose from, most people go for Sulfate or chloride but I don’t like either and wouldn’t want chloride in steel boilers.