Calcium Hardness Drop Test (1 drop = 10 ppm)


When dispensing reagents from dropper bottles, always hold bottle in a vertical position.


  1. Rinse and fill 25 mL sample tube to 25 mL mark with water to be tested.
  2. Add 20 drops R-0010 Calcium Buffer. Swirl to mix.
  3. Add 5 drops R-0011L Calcium Indicator Liquid. Swirl to mix. Sample will turn red if calcium hardness is present.
  4. Add R-0012 Hardness Reagent dropwise, swirling and counting after each drop, until color changes from red to blue.
  5. Multiply drops of R-0012 Hardness Reagent by 10. Record as parts per million (ppm) calcium hardness as calcium carbonate (CaCO3).



I didn’t take photos of the red stage since I hadn’t planned on blogging about this. It starts off red and shifts to purple, but the most critical part is when it turns blue and stops changing color completely. I will make sure to capture and add the red phase next time!


Note: When high calcium is anticipated, this procedure may be used:



Note from Taylor Tech Support:


The tiny specs floating around in the pictures are caused by magnesium in the sample. The magnesium bonds to the indicator and form these specs that float around the water. This interference does not cause inaccurate results. The results will still be accurate.


If you are getting a purple endpoint, it could be a few things but adding 5 or 6 drops of R-0012 to the sample before adding the buffer and indicator, then proceed normally with the test. Include the drops of titrant added at the beginning of the test when counting the total number of drops required to reach the endpoint. If this does not remove the interference then the sample is purple from magnesium.


Although a blue endpoint is what is written in the instruction, the hardness test can be accurate with an endpoint of purple or blue. As long as the purple color does not change anymore with the addition of R-0012. It is important to make sure that the endpoint you are getting is the final endpoint so once color stops changing, the endpoint is reached.