Milwaukee pH600AQ Digital pH Pen

I tried pH meters that cost 5 times what this one does, but this is my fave. It's robust, easy to calibrate, economical, and has lasted me almost 3 years already. It dried out a couple of times between grows, but after an overnight soak in storage solution (or nutrient mix) it has continued working without a hitch. I do re-calibrate if it dries out and needs to be re-hydrated. I also re-calibrate every couple of weeks, or if I drop the unit on the floor, or if I notice a change in how much pH-Lower I'm using. It displays 1/10's, which is plenty accurate enough for most purposes. Get a bottle of calibration solution at the same time so you don't have to pay separate shipping. You will need to calibrate before the first use. I haven't been using the storage solution, instead a few drops of my nutrient mix in the cap has worked fine. I highly recommend this pH tester.