TDS meters only measure ionic silver strength in colloidal silver solutions, not the full colloidal silver strength, since colloidal silver consists of suspended silver particles. A more accurate way to determine the parts per million of silver in a colloidal silver solution is to use a multimeter set to milliamps to measure the current passing through one of the silver rods during production. This current value can then be entered into a calculator along with the volume of water to estimate the production time needed to make the colloidal silver solution.