Problem with Bluelab PH pen

You have to hold cal button down for a bit for calibration to begin at 7 and at 4 to calibrate. Read the directions again

Hi there Give it a good clean make sure the sensor isn’t dirty, Also if you have tested it in the same solution before without cleaning it thoroughly you could’ve adjusted the liquid slightly, re test in new liquids Best of luck 🌱

How old is this unit? I’ve had so much bad luck with pens that I have a 0 grave yard of bluelab and Hanna hydro that I switched to strips. My advice is to take it to the grow shop and have them look at it. OR just see it it is correct with another meter or strips

what heavy hittah said! the solutions are temperature sensitive, too. So make sure you take that into account

You need to take the pH 7 reading . Then take another reading with pH 4. There will be a tick on the screen to confirm it's been calibrated with pH 7 and pH 4 fluid.

This happens on my Apera from time to time... if it stays there, just accept it and go on to calibrate at the 10pH ... it will be just fine! I think what's happening is that the pen is telling itself "gee, I've been reading the 4pH too high" so the OLD 4.5 reading will now be the NEW 4.0 reading... You can always call Blue Lab and double check - but I think you'll find it's nothing to worry about. Cheers!