PH probe calibration
 

How offen, does a PH probe have to be calibrated?

That is something you will probably get a lot of opinions on. I think once every 3 months is absolute minimum, and I think once a month is good practice.

It also depends on the quality and age of the probe. Once a month might be necessary for some while others won't change much over 3 months. Neptune and Milwaukee have worked well for me. American Marine was a big disappointment and Aqua Digital fell somewhere in between.