Searles Soil pH Test Kit is a simple, easy to use pH test kit to help achieve optimum growing conditions. The Searles Soil pH Test Kit method is based on research from CSIRO and does not require calibration when purchased as this is done within a laboratory setting when the kits are manufactured. This home test kit is designed to be used on soil only as the liquid in the kit reacts with soil allowing a pH indication when the powder is applied. As with all chemical products it is to be stored in a cool, dry place out of bright light. Chemicals can break down over time and old test kits can give false reading, so if your kit is more than a year old we recommend replacing it with a new one to provide a more accurate result. The soil sample for testing should not be obtained from the surface of the pot or the garden. The best sample to test is located 5-10cm below the surface, in the well mixed areas.