Product Short Description: Indicator Parameter RED - BLUE Product Description: In the titration of calcium and magnesium with EDTA the indicator calmagite works in the following way. When a small amount is added to a solution containing magnesium at pH 10, red MgIn– forms. As EDTA titrant is added, free magnesium ions in solution react with it. After all the free magnesium is complexed, the next portion of EDTA removes magnesium from the indicator complex, converting the indicator to the blue HIn2– form.