I do the same as Josh and Chubb . I just bought a new probe replacement for my pen . Readings are all over the place after calibration. Plus you know about what you have to add each feeding anyway if you use the same nutes and water. I love my Apera PH60. Got the thing for free from Amazon a while back. They lost it in transit. They said they could not find it so they refunded me and 4 days later  Santa Claus (UPS) delivers the pen. This has happened twice the other was my auto water . Got to love logistics lol