The One Year Alert Combo pack combines a year supply of Ammonia Alert® (1 card) and pH Alert® (1 card and 1 replacement sensor). Ammonia Alert® and pH Alert® are almost half the size of competing products. At 1.5" x 2.5", they are small, clear, and unobtrusive, so they won't detract from the view of your aquarium. Simply place Ammonia Alert® and pH Alert® visibly anywhere in the aquarium or filter. It’s that easy. No chemicals or test procedures are required.