Ammonia Alert and pH Alert employ Seachem Sensor Technology, a sensor changes color reversibly to alert you to shifts in ammonia levels and shifts in pH levels respectively. pH Alert is a unique color device designed to be placed in the aquarium or filter and monitor pH continuously. A sensor changes color reversibly to alert you shifts to in pH levels between 5.8 and 8.2. No tests, no strips, just constant readings. Freshwater Only. Ammonia Alert is an innovative color device for continuously 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 less than 0.05 mg/L (ppm) free ammonia and alerts you to the #1 killer before any sign of stress. It lasts over a year. Marine or freshwater use.