So I've been using the same feed chart for a few grows now so can estimate my ec levels. However I still like to calibrate my pen. I'm using the aquamaster p100 ec and ph pen.

It's a new probe on a 7 month old pen and was calibrated when i changed the probe for pH and ec and all wad good.

I've since used the pen for about 4 weeks on the new grow and have been getting expected ec readings with my feed chart I've been using.

I still like to periodically calibrate but when calibrating ec with 1.41 calibration fluid it's showing 1.8 and even if i try to calibrate it gives me an error message. I've tried new ec calibration fluid and getting same results. I've cleaned my probe and again the same.

Don't think it's a faulty probe as I'm getting expected ec levels with the amount of nutrients I'm using in my feed and as mentioned it's a new probe. But checking against known 1.41 it's showing 1.8.

Anyone had a similar problem?