Why do the hardness titration and colorimetric test results not match?

Document ID

Document ID TE302

Version

Version 4.0

Status

Status Published

Published Date

Published Date 08/16/2018
Question
Why do the hardness titration and colorimetric test results not match?
Summary
Colorimetric and titration methods for hardness give different results
Answer
The colorimetric hardness test using calmagite indicator, Hach Method 8030, was designed for ultra-pure water or water that has been softened to remove hardness. This method was designed to measure low levels of hardness using a colorimeter or spectrophotometer at concentrations less than 4 mg/L (as CaCO3).

When the hardness concentration is well above 4 mg/L, this method may indicate an incorrect concentration. To see if this is the case, measure the hardness in the sample by titration using a test kit or buret. If the titration indicates that the hardness is much higher than 4 mg/L, the result using the colorimetric test may be incorrect. In this case dilute the sample using good quality deionized water to obtain a correct result with the colorimetric method. Then multiply the displayed result by the dilution factor.

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