1x Bluelab pH 7.0 - 250ml 1x Bluelab pH 4.0 - 250ml pH instruments must be cleaned and calibrated at least monthly to provide you with the most accurate reading. pH measuring equipment is calibrated to pH 7.0 first (buffer) then to pH 4.0 (slope). Essential for use with all Bluelab pH products for the calibration of Bluelab pH Probes. To ensure solutions remain accurate: · Avoid cross-contamination · Decanter into a smaller plastic cup · Discard sample after use · Store in a cool dark place · Store with lid secured tightly · Keep out of reach of children Bluelab solutions are manufactured specifically for Bluelab products are NIST certified and are made to a traceable standard to ensure your Bluelab products last longer and maintain accuracy.