Hey FF, I use a Hannah HI98129 to measure PH and so far I've had great experience with it.
I've also replaced the probe on this pen due to an accident, I was swabbing it too hard with a q-tip, and that cost me about $48 off amazon. All I use is storage solution and cleaner solution when gunk builds up around the electrode, no calibration solution needed so far.
http://advancedtechlighting.com/phppmmeters.htm