Calcium without Chloride/Sulfate/Carbonate

I came across a thread on another forum where Martin commented on a water profile for Vienna lager. The "authentic" water was below 50 ppm in calcium, and a brewer who increased the calcium with additions of either CaCL2 or CaSO4 would end up with elevated levels of chloride or sulfate compared to the Vienna water.

What would be a food grade alternative that would raise only the calcium?

you can't raise Ca without also raising another ion.

But you can add Ca w/o adding Cl, SO4 or HCO3. One option is Calcum lactate, which is chalk or pickling lime dissolved in lactic acid.

You can't raise only the calcium - the double positive charge on each calcium ion has to be balanced by two negative charges from some anion or anions. Thus you need calcium salt of something other than sulfuric or hydrochloric acid. Phosphate and lactate come to mind as the only practical ones. You are limited in how much phosphate you can add by the very low solubility of apatite (the phosphate of calcium) and by the flavor of other acid anions such as lactate or citrate.

As you can't buy calcium mono or dibasic phosphate or calcium lactate from your LHBS (but you can from Sigma or, in the case of the lactate from a health food store) it is probably easiest to add lime (Ca(OH)2) in amount sufficient to contribute the desired level of calcium and then add phosphoric, lactic, citric.... acid in the amount required to restore the pH to the desired level (presumably mash pH).