I asked for Bicarbonate as well in the report but was given a report on alkalinity: 84 mg/l
If you put 100 mg of CaCO3 in a beaker with 1 L of water and then bubble CO2 through the beaker until the pH of the water reaches 8.3 and then send that water off to an analyst requesting an alkalinity report he will take the liter of water and add 1 N strong (hydrochloric or sulfuric) acid to it until the pH is 4.3 and then tell you how many mL of acid it took to get there. The molecular weight of CaCO3 is 100 so there is 1 millimole of CaCO3 in the beaker. It reacts with the CO2 by CO2 + H2O + CaCO3 --> 2HCO3- + Ca++ IOW 2 mmoles of bicarbonate ion are produced. When the analyst adds the strong acid its protons react with the bicarbonate ions to produce CO2:
2H+ + 2HCO3- --> 2CO2 +2 H2O
At pH 4.3 nearly all the bicarbonate is converted and as the equation shows to convert the 2 mmoles of HCO3- takes 2 mmoles of H+. Normal (1 N) acid contains 1 millimole of H+ per CC so 2 mL would be required. When the analyst tells you it took 2 mL of acid to reach pH 4.3 he is telling you that the alkalinity is 2 mmol. When talking about charged ions chemists often speak of 'equivalence' which is the number of moles of charge. Normal (1N) means there is 1 mmol of hydrogen ion charge in the acid. If it is HCl there is one hydrogen ion per molecule of HCl so the strength of the acid is one mole per cc. If the acid is H2SO4 then there are two hydrogen ions per molecule so the concentration is 2 mmol/cc. That's why equivalence is used. We don't need to know what the acid is - only the hydrogen ion charge per cc.
So the alkalinity of your water is 2 cc normal acid. Everywhere else in the world this would be reported to you as '2 milliequivalents per liter'. In the US water industry it is traditional to specify not the true alkalinity but the amount of calcium carbonate from which it came given that this was dissolved by CO2. This is done because in most natural waters that is the mechanism by which limestone dissolves. Thus we take the true alkalinity (2 mEq/L) and multiply by 50 and report the alkalinity as '100 mg/L as CaCO3'. This has resulted in lots of confusion to many people but its like measuring distances in feet, yards and miles. That's how we do it and just as there is a fixed conversion between the metric and English systems (one inch is exactly 2.54 cm) there is a fixed conversion between mEq/L and ppm as CaCO3 i.e. 50.
Now on to the calcium. Our 1 mmol/L CaCO3 releases 1 mmol of Ca++ ions at pH 8.3 but as the charge is plus 2 on each calcium ion that is 2 mEq/L. Again we multiply by 50 and say that the 'calcium hardness' of this water we made is 100 ppm as CaCO3. In summary: add 100 mg limestone to 1 L of water and dissolve with CO2 continuing exposure to CO2 until pH 8.3 is reached and you have water with alkalinity of approximately (there are some details I've glossed over) 100 ppm as CaCO3 and hardness of exactly 100 ppm as CaCO3.
Magnesium was outputted as 20 mg/l Caco3 (why?)
Were on a roll here. Now lets put 1 mmol of magnesium carbonate in a beaker, add the liter of water and do the same thing with CO2. When we get to pH 8.3 we again have 2 mmol (2 mEq) bicarbonate but now 1 mmol (2 mEq) Mg++ ion. Clearly then the alkalinity is again 2 mEq/L (100 ppm as CaCO3) and now the magnesium hardness is 2 mEq/L which we again, multiply by 50, giving 100 ppm as CaCO3. So the answer to 'why?' is that this is the way that we report ion concentrations for bicarbonate, carbonate, magnesium and calcium in the US.
You noted that you had asked for bicarbonate but got an alkalinity report. Labs don't measure bicarbonate. They measure alkalinity (as described above). To measure bicarbonate is much more difficult than the simple test I described. In most natural (and all potable) water at pH that meets WHO standards the only weak acid is carbonic and we can look at the water we made earlier with its 100 ppm as CaCO3 alkalinity and note that it had 2 mmol of bicarbonate in it. As the molecular weight of bicarbonate ion is 61 we can then say that the bicarbonate content of this water is approximately 2*61 = 122 mg/L. It is fortuitous that a couple of mathematical effects cancel one another such that this approximation is good between pH's of say 5.5 and 8.3 or so. Above 8.3 some of the alkalinity comes from hydroxyl ions and it falls down. So if your water isn't too weird take alkalinity, divide by 50 and multiply by 61 to get and estimate of bicarbonate. Note that water calculations are done with alkalinity numbers - not bicarbonate. Some of the spreadsheets don't make this important distinction. We had a guy on here wondering why, when he added lime (calcium hydroxide) to RO water (no bicarbonate), his spreadsheet showed the water had a lot of bicarbonate in it.
So, am I missing anything to help my water chemistry for mashing/sparging?
Yes, a whole lot but everyone starts out that way. Full understanding takes quite an investment in time and effort as perhaps just this discussion illustrates.
