PH Tester worked like clockwork for about 4 days after calibration, then it failed and became very inaccurate. The package contains enough ph calibration pack for one calibration, after that you do it yourself. This is a problem because the instructions that came with the digital PH tester list several ways to change the accuracy of the device and require recalibration . "Note: Recalibration is required under the following conditions: Long period of inactivity. The accuracy requirements are very high. The cal (calibration) button was pressed and the electrode was exposed to air for an extended period of time. - Ph Manual These reasons ensure that the device needs to be recalibrated at semi-annual intervals to remain accurate. However mine only lasted about 25-30 tests before the numbers started to fluctuate when out of the water and as soon as it was put in the water it stopped contracting but its readings were off by a few points. It's a shame. I liked it while it worked, but I don't recommend it to others.
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