Phoenix Gravity New Millennium Edition™ filter cartridges are not designed to remove beneficial, healthy minerals from your water. As the natural filtration process leaves essential minerals such as magnesium and calcium in the water, the filter does NOT alter the total dissolved solids (TDS). The TDS therefore remains unchanged, but a TDS value says NOTHING about the quality of the water. For more information, please read the frequently asked question: “What do the readings from a TDS meter tell us?”