Total Hardness vs Alkalinity

[broskobandi]

First of all, we have super hard water which forces me to use way too much acid to lower the mash pH. I learned that boiling then decanting the water reduces the hardness a great deal. This lowers the alkalinity so it will take much less acid addition to lower the pH to the desired levels.
Brewersfriend's advanced water chemistry calculator requires me to enter the alkalinity of my water either as "Bicarbonate" as mg/l OR as "alkalinity" as CaCO3. Now, in my water report that I got from our water supplier, I have two separate items that seem to be relevant, one for "alkalinity" (343 mgHCO3/l) and one for "total hardness" (313 mgCaCO3/l). Which value do you think I should use? Should I just convert my HCO3 alkalinity value into CaCO3 by dividing it by 1.22 and call it a day? But doesn't total hardness refer to the bicarbonate revels? If so, should I use my total hardness value? So many questions...

Thanks!

 

[Bassman2003]

This was always confusing. I am looking forward to hearing the answers.

 

[whattabrau]

Hardness is [effectively] Ca+Mg. It has nothing per se to do with alkalinity. Add a ton of gypsum to DI water and you have hard water with no alkalinity. If you dissolve CaCO3 (with CO2) you end up with both hardness and alkalinity, which is probably where the confusion arises, plus from the "as CaCO3" unit.

I guess you can just enter the mg/L HCO3- for your alkalinity. Notably, you can't convert mg/L HCO3 to alkalinity without knowing the pH, but especially if the water pH begins with a 7, it's "close enuf". You should be able to just input Ca and Mg separately for hardness.

 

[Cheshire Cat]

This was always confusing. I am looking forward to hearing the answers.

I totally agree. I do water treatment based on what Brewfather tells me to do. I know the profile of my source water and select the beer type for the finished water. However my understanding is low especially around alkalinity I.e. does acid reduce alkalinity or pH or both?

 

[whattabrau]

However my understanding is low especially around alkalinity I.e. does acid reduce alkalinity or pH or both?

Yes. When you add acid, the carbonate alkalinity turns into water + CO2, but it happens gradually, i.e. you need the pH to get lower and lower for more and more of it to happen.

 

[Cheshire Cat]

Yes. When you add acid, the carbonate alkalinity turns into water + CO2, but it happens gradually, i.e. you need the pH to get lower and lower for more and more of it to happen.

Merci

 

[broskobandi]

Hardness is [effectively] Ca+Mg. It has nothing per se to do with alkalinity. Add a ton of gypsum to DI water and you have hard water with no alkalinity. If you dissolve CaCO3 (with CO2) you end up with both hardness and alkalinity, which is probably where the confusion arises, plus from the "as CaCO3" unit.

I guess you can just enter the mg/L HCO3- for your alkalinity. Notably, you can't convert mg/L HCO3 to alkalinity without knowing the pH, but especially if the water pH begins with a 7, it's "close enuf". You should be able to just input Ca and Mg separately for hardness.

Thanks for the explanation, it starts to kinda make sense.
So, you are saying that I should use the mg/L HCO3 for alkalinity. But, do I enter it as "bicarbonate as mg/l" or as "alkalinity as ppm as CaCO3"? This calculator has these two options. And the fact that other sites such as brewfather's water chemistry calculator doesn't even have this many options for entering alkalinity makes things even more confusing...

I did try and just say "whatever, 313 and 343 are close enough to each other, I can use whichever", but it actually does make a huge difference in terms of how much calcium I need to add for preboiling and then decanting my water before the mash.

Brewersfriend does not ask for total hardness but Ca and Mg separately so that is not an issue. The fundamental question is, is it the alkalinity or the total hardness value that I need to use for brewersfriend's water chemistry calculator's "alkalinity" field and should I enter the value as "bicarbonate as mg/l" or as "alkalinity as ppm as CaCO3"?

 

[whattabrau]

Thanks for the explanation, it starts to kinda make sense.
So, you are saying that I should use the mg/L HCO3 for alkalinity. But, do I enter it as "bicarbonate as mg/l" or as "alkalinity as ppm as CaCO3"?

bicarbonate == HCO3, so take a wild guess ;-)

Alkalinity "as CaCO3" is a fictional unit and means how much alkalinity you'd get if you added that much CaCO3. If you add for example potassium carbonate (K2CO3), you'd still get "alkalinity as CaCO3", but you wouldn't have added any CaCO3. So, it's a bit like measuring the mass of fruit "as apples": you could still use it for oranges, as long as you agree that "an apple" is e.g. 250g. So, 600g of oranges would be 600/250 = 2.4 "as apples".

The fundamental question is, is it the alkalinity or the total hardness value that I need to use for brewersfriend's water chemistry calculator's "alkalinity" field and should I enter the value as "bicarbonate as mg/l" or as "alkalinity as ppm as CaCO3"?

alkalinity, and you can pick either "mg/L HCO3" or "as CaCO3". You can calculate one from the other, though like I already said, strictly speaking you should also know the pH, but it doesn't matter all that much. My software actually asks for it in mEq/L [and pH], which I find to be a unit that I can wrap my brain around. I guess I don't like apples.

 

[broskobandi]

Amazing, thank you very much for your reply!