To expand...from a chemical engineering source:
"There is NO
relationship between pH and TDS
. Let us imagine a solution of an acid salt, say sodium bisufate (a.k
.a. sodium hydrogen sulfate). No matter what its concentration (TDS
), it will have a low ph (< 7.0). Now take an alkaline salt solution, say sodium carbonate. Again no matter the concentration, the pH will be high (>7.0). Even for a given solution, there is nothing approaching a linear relationship. Take pure water and drop a flake of sodium hydroxide into it. The pH will skyrocket. As you add more caustic, the pH will continue to rise to a point, but it will do so much more slowly."