Never bothered to check my run off. My ppm normally stay around 7-900 I probably locked her out at some point when I assumed calmad definitely cause I backed off my base nutes to jack up the cal mag. I tend to keep my feed scheduled the same though out bc I know the recipe to stay between 6.1-6.4 ph. I use my pen so little because I know what stable is they always lose calibration when I need them most. Gonna go organic my next few runs while I get back to work and invest in a blue lab with the shelf stable calibration fluids