do you know you need to adjust the water temp with those cheap ones before you take a reading? if your not doing it the ph wont read correct.I use the cheap 10 dollar yellow hanna copies from china. Work well. Calibrate once a month. Never off by more than .2, andthat was after 4 months of sitting in a box dry. replacement probes are cheap so when you notice it fucking up you can swap em out. Mine has been good for a year and not problems.