Is it possible to guess at ppm Ca and Mg from only ppm TDS?

[Silver_Is_Money]

The reason why we are concerned about predicting Ca and Mg is that mash pH adjustment assistant software is only concerned with Alkalinity, Calcium, and Magnesium, and it ignores all of the other ions with respect to predicting mash pH. I'm not sure if I mentioned this already.

 

[AHarper]

The reason why we are concerned about predicting Ca and Mg is that mash pH adjustment assistant software is only concerned with Alkalinity, Calcium, and Magnesium, and it ignores all of the other ions with respect to predicting mash pH. I'm not sure if I mentioned this already.

Ah that might explain why on my last recipe build I adjusted for a 5.4 mash pH - using Phosphoric acid this time instead of Acidulated malt - and my measured mash pH turned out to be 4.3! Despite the calculator working it out to be 5.4.

I went with that value as I didn't see any quick way of adjusting it back to 5.4 - I don't even know if I should have anyway.
The beer is now in the fermenter so it is in the lap of the gods now anyway.

 

[Minbari]

Wall-Mart is a LONG way off for me to get it delivered. I'm in the UK and their equivalent store is ASDA - and they don't sell RO water.

Plus I bet the shipping would be killer! Lol.
Can always use distilled?

 

[Donoroto]

Lidl in the US sells distilled water for under a dollar a gallon. Alan, I know there's a Lidl in Brighton somewhere?

 

[AHarper]

Lidl in the US sells distilled water for under a dollar a gallon. Alan, I know there's a Lidl in Brighton somewhere?

That's where I get my Chase Spring water. £0.17 for 2 lt. That's about $0.14 a quart.... I asked them to sell it in gallon (5lt) containers but no luck yet. That's why I have 100+ 2lt bottles in the garage lol... I get a large shopping trolley full at a time.
I may change over to ASDA (UK Wall Mart!) water as it is less mineralised but more expensive. The only problem is where to store it...

 

[Donoroto]

I sense a plan for a stainless water tank above the garage...

 

[AHarper]

I sense a plan for a stainless water tank above the garage...

Don't think that hasn't been thought of... My garage is getting pretty cramped. It's mostly beer making kit of one sort of another

 

[Silver_Is_Money]

Scant data. Quoting the words of everyone's favorite robot, Johnny 5:

Need input!

That said, my first revisions (subject to further revision of course) to the empirical method are as follows (see highlighted):

Total Hardness (as CaCO3) ~= 0.85 x ppm_TDS (as read via the TDS meter)
Total Hardness (as CaCO3) = 2.5(Ca++) + 4.12(Mg++) (this, with the constants rounded, is a truism)

~68% of Total Hardness comes from Ca++ (on loose average/approximation for fresh water)
~32% of Total Hardness comes from Mg++ (on loose average/approximation for fresh water)