Do not blindly trust in the results of your test kits or electronic testing devices. While most of them are designed to be fairly accurate, their ability to measure parameters depends greatly on a number of things. For example, chemical reagents of the test kits can expire, and most do so after a relatively short time. Additionally, some of these tests require a strict adherence to testing procedures. If you deviate even a little, the results could be way off. If you prefer to test water parameters yourself, as opposed to sending them off to a professional water testing service, make sure you have a good understanding of how the tests work and make sure that all equipment is calibrated properly and chemicals are well within their expiration date. If your testing cannot repeat the results after multiple tries, then something is wrong.