Hardness Test Kit

Water hardness has traditionally been defined as the capacity of water to precipitate soap. The ionic species in the water causing the precipitation was later found to be primarily calcium and magnesium. In the present, therefore, water hardness is actually a quantitative measure of these ions in the water sample. It is also now known that certain other ion species, such as iron, zinc and manganese, contribute to the overall water hardness. The measure and subsequent control of water hardness is essential to prevent scaling and clogging in water pipes.

The APPIA HD test kit tests the hardness level as mg/L (ppm) calcium carbonate, via an EDTA (ethylene-diamine-tetraacetic acid) titration.

Testing

To perform a drop test, simply fill a test cell with sample water, add buffer and indicator reagents, and swirl to mix. The sample will turn red if calcium hardness is present. Next, add the calcium hardness reagent, swirling and counting each drop, until the color changes from red to blue. Finally, multiply the number of drops used by the equivalence factor in the test instructions to determine the calcium hardness level. The reading is expressed as parts per million of calcium carbonate.  

 The color progression in a hardness test is from red, to a mixture of red and blue, to blue. To be certain the color change is permanent, indicating you have reached the true endpoint, add one more drop of titrant. If the blue color remains unchanged, do not count this drop.

Beware the Fading Endpoint

 

Occasionally when testing calcium hardness you may get a purple endpoint instead of blue. This is called a "fading endpoint" and is due to interference from metal ions (most likely copper from algaecides, pipes, or source water). Retest, but prevent the interference by adding five or six drops of hardness reagent to the sample before adding the buffer and indicator. Then proceed as usual. Remember to count the drops of titrant added at the beginning when you calculate the total number of drops required to reach the endpoint.

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