OPTIMAL CHOICE: The ACME pH 4 and 7 buffer solution is essential for measuring the pH level of any substance with a meter and electrode. These professionally made pH buffers are stable and resistant to change, so you can obtain accurate results every time. READY TO USE LIQUIDS: Our pH 4 and 7 calibration solutions are ready to use and do not require dilution. PREMIUM PACKAGING: The products come in heavy-duty gallon containers. No need to worry about leakage during shipping. Each gallon will have a lot number and expiration date. QUALITY STANDARD: All of our pH buffers are traceable to NIST (National Institute of Standards and Technology, USA) UNIVERSAL SOLUTION: These pH calibration solutions can be used with most pH meters. pH 7 is color coded yellow. pH 4 is color coded red.