Acavia wrote:So if I used Potassium bicarbonate for my water's alkalinity, I would use 119.1525% (100/84.01) more potassium bicarbonate than what the sodium bicarbonate amount would have been for the same alkalinity level?

Yes. 119 grams of KHCO3 has the same number of molecules as 100 grams of NaHCO3. And it's the number of bicarbonate molecules that determine your alkalinity.

P.S.
When comparing bicarbonate to carbonate molecules there is a wrinkle. Carbonate molecules, like CaCO3 can neutralize two H+ ions, and bicarbonate molecules, like KHCO3 can only neutralize one H+ ion. That's why 1 mmol/L of KHCO3, which weighs 100 mg/L has only 50 mg/L alkalinity in CaCO3 equivalents, whereas 1 mmol of CaCO3, which also weighs 100 mg/L has of course 100 mg/L in CaCO3 equivalents.

So it is twice the 119% to get an equivalent buffer? So I really would need 2.238 times more potassium bicarbonate as sodium bicarbonate? I do not think that what you are indicating but I am not absolutely sure, so I want to make sure.

Acavia wrote:So it is twice the 119% to get an equivalent buffer? So I really would need 2.238 times more potassium bicarbonate as sodium bicarbonate? I

No, 119% is the correct mass increase to get the same buffer (alkalinity) from KHCO2 that you would get from NaHCO3. Either one of those molecules can neutralize one H+ ion. The KHCO3 molecule is a little heavier, so that's why you need a little more of it weighed in grams.

It's only when comparing bicarbonates (KHCO3, NaHCO3) to carbonates (CaCO3, MgCO3) that you need to allow for the fact that one molecule of carbonate will buffer twice as much acid as one molecule of bicarbonate.

I thought so, but just wanted to make sure. Thanks.