No tests, no strips. Lasts up to 4 times longer than competitive products. Continuously monitors pH in freshwater. pH Alert is a unique color-changing sensor designed to be placed in the aquarium or filter to continuously monitor pH. A sensor reversibly changes color from yellow to orange to red alerting you to pH changes between 5.4 and 8.0. For freshwater use only. pH Alert lasts up to 4 times longer than competitive products and is half the size. It is compact, clear and discreet, and will not detract from the aesthetics of your aquarium.