Not necessarily. If your meter is 500 scale (most common in NA) it is calibrated to NaCl as an ~actual ppm. Other salts/elements will have different conductivity. Your actual ppm for the dGH and dKH readings calculate close to 400ppm and the particular elements in those two readings may be better represented on a 700 scale meter. It gets messy because of the many variables and the confusion over the 500 vs. 700 scale meters. 700 scale meters are calibrated to KCl. The basic question is: is your mix of elements better represented by NaCl or KCl? Only you can decide. Many hydroponics people believe that KCl is a closer comparison to our nutrient mixes. it is because of this matrix of variables that TDS meters are better used as relative guides as opposed to telling us what actual ppm is, and they are useful for such a purpose.The TDS of my tap water is 510 ppm. Recently the GH was 6.0 degrees and the KH was 5.1 degrees. So there's a lot of other stuff going on in my tap water. It's not just Calcium and Magnesium. But I lived somewhere else that had phenomaly hard water. I remember it taking fifty drops of GH test reagent to get the sample to change from red to blue. So in your case it might actually be just a whole lot of Calcium and Magnesium. Simply phenomenal. I'm really tired of RO water too.
