Hey, while i am not a professional i noticed that test strips are not always very accurate. In my tank i use the "JBL Pro aquatest combi set". It's a very quick and easy to use water testing kit, i really recommend this one. If your interested here is the link to the test kit also: https://www.petsplace.be/nl/jbl-proaquatest-combiset-plus-nh4-testen-4014162240903-pps?srsltid=AfmBOoqVEjFOZT9UDNiKmV88aRgDoqfaxOnJlNvh5Oohl8sV7e85jMcnYoU