To make high ppm colloidal silver, the water should be heated, and the reducing agent must be added at the beginning of the process. Then the ionic silver is being reduced as it is being made and will not go over its solubility limit. For 40 ppm, you can use maltodexrin, or cinnamon extract as the reducing agent and stabilizer. For really high ppm like 320, knox unflavored gelatin works best.
For plain 20 ppm ionic silver, you can make that cold with only the electrolyte in the water. With SilverTron Elite Ver 2, you can also make 20 ppm ionic silver with nothing added, but it will take a long process time.
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