- Bluelab pH 4.0 Calibration Solution 20 ml Sachets
pH measuring equipment must be cleaned and calibrated regularly to ensure they are giving the user accurate readings. pHæinstruments areæcalibrated to pH7.0 first (buffer)æthen to pH4.0 (slope). Bluelab's EC/CF equipment does not need calibrating as they are all factory calibrated. The CF27.7 (EC2.77)æsolution is used as a reference or checking solutionæto ensure you have adequately cleaned the EC/CF probe.