Specification: 100% brand new with high quality 5x 4.01 solution (potassium hydrogen phthalate) 5x 6.86 solution (mixed phosphate) 5x 9.18 solution (borax) No need to measure, just mix each packs with 250mL distilled water. The set includes 5 package of 4.01, 5 package of 6.86 and 5 package of 9.18 calibration solution powder for all pH needs. Individual sized packets can be tucked in drawer, bag or suitcase for travel. Great for testing pH balance of drinking water, pool, aquarium, RO system, Spa, or hydroponics. How to use: Completely empty the powder into a clean 250mL glass beaker. Add 250mL deionized water (or distilled water) to the beaker. Stir until the powder has completely dissolved. Follow the Esee pH meter calibration steps to calibrate your pH meter(Asin for Esee PH meter: B01LWMJVPG ) Package Included: 15 x PH Calibration Powder Note: Please allow minor error due to manual measurement. The colors may be a little difference for the different monitor display.