Seachem pH Alert. Freshwater. 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 8.6. Freshwater Only. DIRECTIONS: Simply place pH Alert visibly anywhere in the aquarium or filter. Its that easy. No chemicals or test procedures are required. When first put in service, response time will be about 30 minutes. Thereafter, pH shifts will register within ten minutes. The life of the pH Alert sensor may vary depending on a variety of tank parameters. A replacement sensor is included to ensure effectiveness for 3 to 6 months. Sensor exhaustion is indicated by a visible fading or washing out of sensor color. To apply replacement sensor, first peel exhausted sensor from reference card. With tweezers, remove the paper backing from the new sensor to reveal adhesive. Apply new sensor to reference card. Press it firmly. Avoid touching sensor surface with fingers.