Always follow the instructions in the manual. To test hardness using API 5-in-1 Test Strips, dip a strip into your water sample for 2–3 seconds, then remove it without shaking off excess water. Hold the strip level and wait 30 seconds for the colours to develop. Compare the hardness test pad (usually labeled GH) to the colour chart on the package. Match the colour to determine the general hardness (GH) level in ppm. Make sure to read the strip within the recommended time for accurate results. Always store strips in a dry, cool place to keep them effective.