These test strips measure ammonia (NH3/NH4+) dissolved in water. The strip is comprised of 2 pads. The first absorbs a small amount of water & converts the dissolved ammonia into a gas. The gas then reacts with chemicals in the second pad which causes a color change. This pad is compared to the color chart & should indicate a concentration in the 0-100ppm range.
Click on the Details tab below to see an enlarged version of the color chart.