Hi. I've been playing with the Basic Water Chemistry Calculator and want to know if there is an error for CaCO3 additions. It seems the reported Ca++ amount is 1/2 of what it should be. For example, go to the calculator and select 1 liter for water volume. Do not have any default salts from a water source (keep all the those fields blank). Then go down below and enter 1 gram of CaCO3. Since CaCO3 is ~40% Ca by weight (anhydrous), you would expect to have 400 ppm Ca++, but it is only 200 ppm. Also, the sum of Ca++ and CO3 (or HCO3 as it's reported) should be ~1000 ppm, but it's not. All this assumes CaCO3 source is anhydrous. Can someone explain or check this out? If the calculator is incorrect, it needs to be fixed. If it is correct, then what are the assumptions about the CaCO3 (Chalk) composition. Again, if correct, it would have to be ~50% water or some other material - but if it has other salts to an appreciable extent (an impure source), they are not displayed and accounted for. All the other salts give the correct numbers either as anhydrous or hydrated forms based on simple MW calculations.