I started my current grow with drops. After a week of veg I bought a HM meter and calibrated it. I was keeping my nutrients at roughly 5.5-5.8 with drops. When I checked it with my new calibrated meter it was reading 6.9. I recalibrated the meter to 4 instead of 7 and still pH was 6.9. I then adjusted nutrients down to 5.8 with the new meter. I’m still curious as to why the drops were so far off? The color difference between say 5.5 and 7 is a very noticeable difference. Did I contaminate solution somehow? Plants are doing great and nutrients hold steady at 5.8 with ppm of 750.
HM meters are dog shit. Sorry to be the bearer of bad news. Had a buddy go through 2 of them in a week. Wouldn't calibrate or hold worth a shit.
I'd suggest Bluelab. Ive used Oakton with zero issues. Others will prob have suggestions also. Had bad luck in the past with Hanna stuff. Always drops also like others stated. Bluelabs went up some recently.