Which of the following is NOT a type of water conditioner?

In the context of water conditioning, the focus is on substances that help manage water hardness or improve water quality for various applications. Borates, sodium citrate, and EDTA (ethylene diamine tetraacetic acid) are all types of water conditioners.

Borates are used to soften water and can help prevent corrosion. Sodium citrate serves to chelate metal ions, reducing hardness and scaling. EDTA is a powerful chelating agent that binds with metal ions in the water, thus improving its quality by removing unwanted hardness.

Calcium carbonate, however, is not a water conditioner but rather a compound that contributes to water hardness. It forms scale and can lead to problems in water systems, rather than improving the quality of water or softening it. Therefore, it is appropriately identified as the option that does not fit the category of water conditioners.