This might be of interest:
The term total dissolved solids (TDS) refers to the sum of all cations or
anions, measured in parts per million as calcium carbonate.
Parts per Million (ppm)
The weight to weight ratio of any ion to water.
Calcium Carbonate Equivalent
Due to the differing molecular weights and valences (charges) of ions, a
meaningful total of all the ions present in water can be calculated only when
all of the ionic concentrations are brought to a common denominator. This
common denominator is known as the calcium carbonate equivalent.
It is quite simple to calculate: first determine the molecular weight of
the ion in question; second, divide this molecular weight by the valence of the
ion to arrive at the equivalent weight; last, divide 50 (the equivalent weight
of calcium carbonate) by the equivalent weight of the ion. This conversion
factor from the last step multiplied by the ppm as ion gives the ppm as calcium
carbonate.
Milligrams per Litre (mg/L)
Like grains per gallon, this can be thought of as a measure of the
concentration of dissolved minerals in a litre of water. It is a weight to
volume ratio, with the weight of the dissolved minerals expressed as calcium
carbonate equivalent.
All the best, Ivan.
