When the concentration is about 3-5 PPM, the phosphate balls can form the soluble complex compounds and insoluble nano-level film to play a scale-preventing and anti-corrosive role to effectively prevent the secondary contamination. The metal ions such as Ca2+, Mg2+, Fe3+, etc. in the water is prone to form the insoluble substances such as calcium carbonate, magnesium carbonate,, etc. in the water pipe wall. The polyphosphates react with the above metal ions to form the soluble complex compound to inhibit the formation of the calcium carbonate (CaCo3) and magnesium carbonate (MgCo3) and form a dynamic protective film when reacting with iron ion to give the scale-preventing and anti-corrosive effect.
The phosphate balls are colorless and odorless.  They are formed through neutralization and melt polymerization at the ultra high temperature (1200-1700 degree centigrade)are harmless to human body when used for food processing or drinking water.  American FDA has it into the GRAS (Generally Recognized as Safe )List.  And its safety has been tested up to standard by Korean National Health Care Academy.