My Oakton pH 6+ meter isn't stabilizing during calibration. It's currently set on USA 3pt. I've left the probe in my pH 7 solution and hit calibrate, but it won't stabilize. I can go ahead and hit enter to get it to say 7.00 but as soon as I try to calibrate again, it reads ~7.48 - ~7.51 when in calibration mode and still won't stabilize. I thought I had it working earlier, but then when I went to use pH 10 solution, it wouldn't stabilize and threw Er 5. same with pH of 4. Does anyone have any experience with this normally VERY simple to use meter?