This Bluelab HD125026 calibration solution CF27.7 (EC2.77) 250ml is used as a reference or checking solution to ensure you have adequately cleaned the EC/CF probe. Bluelab solutions are manufactured specifically to the calibration process and held to high laboratory standards. To ensure an accurate reading, pH measuring equipment must be cleaned and calibrated regularly. This solution must be stored with lids securely tightened, as evaporation will cause salt content in the solution to rise, decreasing the effectiveness of the solution. This solution must also be in a cool place away from direct sun and heat and away from children.