Ph AlertSeachem's 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 of shifts in pH levels between 5.8 and 8.2. No tests, no strips, just constant readings.
Lasts up to 3-6 months, for freshwater only. It's small, clear, and unobtrusive, so it won't detract from the view of your aquarium.