I bought a Hanna HI98129 had it for for a year or so and only calibrated it once.. no issues.. just switched out to a more expensive hanna system that stays in the reservoir at all times.. selling it if your intrested...
if you got space go with a reservoir.. it helps from the ph jumping up and down.. i usually change water every 2-3 weeks.. I just put a hose on the outlet end and let it pump it to the drain.. then pour in new h2o... easy as pie..
I just went out to the local hardware store (jowes, or hme depot) and got one of there systems 150 bucks i think 5 stage.... one thing you gotta think about is how much water do you need filtered a DAY.. and if you are using it for ice maker/fridge water.. yeah the 150 bucks was ok.. but i...