I've been using this Milwaukee pH meter for a couple of years, still ticking. Be sure and get a bottle of calibrating fluid. I don't use storage fluid, just a couple of drops of nutes in the cap after each use:
The Milwaukee Instruments compact pH pen tester is often used to help maintain pools and aquariums as well as improve results for growers and quality in a range of food and beverage uses.
milwaukeeinstruments.com