The HYDROS pH 4.01 calibration solution works on any pH probe, not just the HYDROS brand. We recommend using at least two points of calibration on a monthly basis to allow the sensors to provide the most accurate reading possible. Using 4.01 a single use packet achieves this calibration process. It is helpful to order enough packets to get through 3 months of calibration. Calibration packets can be stored in a cool dry area for up to 1 year.
