Features Continuously monitors pH in freshwater Seachem sensor technology No tests, no strips Lasts up to 4 times as long as competing products Long-lasting, continuous monitor measures aquarium pH level for 3 to 6 months. Redesigned sensor technology allows "at-a-glance" pH readings from 5.8 to 8.2. Simply match pH sensor dot to corresponding color wheel for aquarium peace-of-mind. This pH range is perfect for most freshwater aquariums from soft water, Amazonian to hard water, Rift Lake cichlid environments. Paper-thin pH monitor measures only 1-1/2" x 2-1/2" high for convenient and discreet placement anywhere inside your aquarium.For freshwater aquariums only. More Information Directions Place pH Alert visibly anywhere in the aquarium or filter. It's 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. Sensor exhaustion is indicated by a visible fading or washing out of sensor color.