Corals and other organisms in our tanks reduce alkalinity and we need to replenish it if we want colorful, healthy, growing tanks. Replenishing alkalinity can be as simple as testing now and then and dosing an additive to raise it back up. Many experienced reefers agree that alkalinity is the single most important element to monitor and maintain in our tanks. Alkalinity serves two major roles, first is maintaining the pH (or acidity) of the tank. Second is providing carbonate and bicarbonate, which is the basis for how corals stay healthy and grow. While alkalinity is a generalized term, in the reef tank we are almost always referring to carbonate alkalinity because bicarbonate and carbonate make up a vast majority of the alkalinity in a typical reef tank. This means when I use an alkalinity test, I'm really testing for two things; to ensure the alkalinity is correct so the water can properly buffer and maintain the tanks pH, but also to make sure the water contains enough carbonate to supply the corals and coralline algae to support health, growth and likely coloration. Watch this video to learn more about alkalinity and its effect on your reef tank.