Ammonia AlertTM is an cutting edge color device for frequently detecting and monitoring toxic free ammonia. A sensor changes reversibly from yellow to green to blue, relative to the ammonia concentration. No test kits, chemicals, or procedures are needed. The device detects not up to 0.05 mg/L (ppm) free ammonia and alerts you to the number one killer before any sign of stress. It lasts over a year. Marine or freshwater use.Within the absence of free ammonia the unit will assume a yellow or faint yellow-green color. It’s normal for the dry sensor to have a greenish hue. It is going to take as much as a couple of 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 frequently with a response time of about 15 minutes. Response to decreasing ammonia is slower, requiring about 4 hours to move from TOXIC to SAFE on removal of ammonia.