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-inch by 2.5-inch, 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.