Bluelab pH 7.0 Calibration Solution 500 ml (6/Cs)In Store Location: @E13 Bluelab pH 7. 0 Calibration Solution "pH measuring equipment must be cleaned and calibrated regularly to ensure they are giving the user accurate readings. pH instruments are calibrated to pH 7. 0 first (buffer) then to pH 4. 0 (slope). Calibration Solution should be stored in a cool place out of direct sun and heat. They should be stored with the lids securely tightened."