Review on 🌊 Digital Water Tester for TDS and pH Measurement by Rick Everett

Just received TDS and pH meter. The TDS meter works fine but the pH meter does not. First I measured tap water with it, showed a pH value of 9.5. This is drinking water, the readings are almost like a Na2CO3 solution! So I calibrated to the standards provided: first pH 9.18, then pH 4.01, then pH 6.86. After calibrating the instrument, I returned to test these calibration standards. The readings were satisfactory for pH 4.01 and pH 6.86 solutions, but for pH 9.18 solutions the readings were 0.00. I then attempted to calibrate the instrument again with this pH 9.18 solution; During this time the meter was not calibrated and the reading was held at 0.00. Can you tell me what's going on? Or have to go back.