The pH Buffer Capsules (3x10) kit is a convenient set of three vials containing capsules to make pH 4, pH 7, and pH 10 buffer standards for calibrating pH sensors. Each vial contains 10 capsules, each of which produces 100 mL of solution when mixed with DI water. Add three drops of the buffer preservative to 100 mL of your buffer solution to prolong the shelf life. Hydrion Color Key Buffer Preservative is a combination mold inhibitor and universal indicator for color coding the buffer solutions: orange for pH 4, green for pH 7, and blue for pH 10.