stain inhibitor – A chemical that will combine with dissolved metals in the water to prevent the metals from coming out of solution (precipitating or causing stains). May also be a chemical that removes dissolved metals from water. Leslie's Stain & Scale
a class of chemical compounds that form a loose association with dissolved minerals such as calcium or magnesium. These chemicals help keep the minerals in solution, prevent scale formation and, over time, redissolve scale deposits. Sequestering is the preferred way to treat calcium problems.
a compound that, when added to water, will chemically bond with calcium and other minerals to make them, in a sense, more soluble