Quote Originally Posted by Mr. Clandestine
Did you calibrate the pH pen you used? I don't have a digital pen, but I know that many of them have to be calibrated using a solution with a neutral pH of 7.
Is that right? My oakton came pre-calibrated from the factory. My hydro shop guy told me not to bother. Just incase I bought the calibration solution and tested it out. Came out at 7.0 exactly.

Do you know if this is just something that manufacturers do if they feel like and some manufacturers dont?