As was discussed earlier, chelants are sequestrants that depend upon stoichiometric reactions between themselves and deposit components. Because of the stoichiometry involved, it is usually difficult to justify their use as primary deposit control agents in cooling systems because the calcium levels are often very high. However, chelants such as EDTA and NTA are frequently employed as adjuncts in antifoulant formulations for scale and metallic ion control. Furthermore, they can often be used in high concentrations to assist in cleaning systems which are fouled with some forms of calcium and iron deposition.