if u have the hanna red pen it need's to be calibrated with 7.01 solution. i use gh brand 7.0 it ses error fault or something like that but it gives perfect readings.as far as the difference.its not much,and i wouldnt worry about it.
disrupt86 Reviewed by disrupt86 on . Hanna Ph pen So i recalibrate my Ph pen using the 4.01 and 7.01 solutions. I did the 7 first then the 4, i also have the 10.01 solution but i use either the 4 or the 10, i used the 4 because well my ph is going to be right between 4 and 7 so i figured that would be the most accurate calibrating method. Once all is set and done, i wanted to test how well it was calibrated so i put it in the 10.01 solution and it reads out 9.73.... Is that bad? or is it just calibrated for the low ph? and not for the high ph? Rating: 5