Hi folks, Sorry for the second question-asking post in one day! I just bought test kits for carbonate hardness and general hardness, both of whic give readings only in ppm. Could someone enlighten me as to how these values are converted into the appropriate German units of dKH and dGH ? Many thanks, Marcus. ======== Marcus C. Tate School of Earth Sciences Macquarie University Sydney, N.S.W 2109, Australia mtate at laurel_ocs.mq.edu.au