>Correct me if I am wrong, but I think 1 degree of hardness is equal to >17.9 ppm. >You also have to include both dgh and dkh to equal total dissolved solids. >Let me >know if this is incorrect. > >Tim Total dissolved solids can also include things like sodium chloride, which will not contribute to either general hardness (total hardness to the analytical chemist; Mg + Ca + Sr, etc) or the carbonate hardness (carbonate and bicarbonate alkalinity). Michael Schmidt California State University, San Marcos San Marcos, CA