Originally Posted by whiskeyjack
...you can take total hardness (mine is 157 as CaCo3) and convert it to get both Ca and MG.
Why guess when you have the individual harndesses respectively 103 for calcium and 54 for magnesium? As I showed in #8 you divide "as CaCO3" numbers (calcium hardness, magnesium hardness and alkalinity) by 50 to get the number of electrical charges associated with those ions.
Ca: 103/50 = 2.06 mEq/L
Mg: 54/50 = 1.08 mEq/L
Alkalinity: 80/50 = 1.6 mEq/L
You then multiply by the weight of the ion which has the given amount of charge:
Ca: 2.06*20 = 40.12 mg/L
Mg: 1.08*12.15 = 13.12 mg/L
Alkalinity is a little trickier because the pH is so high in this case. At lower pH you would assume it's all bicarbonate and use 61 as the 'equivalent' weight
Alkalinity: 1.6*61 = 97.6 mg/L bicarbonate
but at pH 9.1 (which is unusually high - out of EPA's recommended range) the alkalinity of 80 yields bicarbonate at 84 mg/L and carbonate at 5 mg/L
The clue that the given number is not 'as the ion' is that it is labeled 'as' something else in what we have discussed so far 'as calcium carbonate'. If a number is not labeled as something else then you can assume it is mg/L of the ion. Other things that often get labeled as something else are nitrate and nitrite which are often expressed in terms of their nitrogen content. Ward Labs is used by many homebrewers and they do this indicating nitrate as
NO3-N and nitrate and NO2-N. In the former case, multiply by 4.43 to get the mg/L nitrate ion. In the case of nitrite multiply by 3.29. Ward Labs also lists sulfate in terms of its sulfur content and labels it SO4-S. Multiply by 3 if sulfate is reported this way.
Sometimes (especially in European literature) you will see hardness expressed 'as CaO'. Sometimes you see phosphate specified 'as P2O5'. In the Ward Labs reports the total of phosphates is expressed in terms of the total phosphorous content.