In the absence of free ammonia the unit will assume a yellow or faint yellow-green color. It is normal for the dry sensor to have a greenish hue. It may take up to a few days for a dry sensor to equilibrate with the water. No sampling of water, chemicals, or test procedures are required. The presence of the free ammonia is detectable continuously with a response time of about 15 minutes.
Free ammonia is much more toxic than ionized ammonia.
Avoid touching the sensor with fingers, since skin oils can damage it. Do not use bleach, soap, detergents or hard objects to clean the sensor. Some dye medications may discolor the sensor. Sensitivity improves with age, provided the unit is not allowed to dry out, however, drying does not permanently impair the unit. For maximum sensitivity, the unit should be read under natural daylight or daylight simulating light.