A fairly common occurrence as chloramine is present in a lot of water supplies to folks homes, well as far as I know for U.K. water supply, donāt know about USA and Australia etc but this is what a lot of keepers call a false reading.
Sometimes youāll get false or inaccurate readings if you use cheap test kits, particularly the dip strip kits, best avoided but better than nothing if you have not the budget, if unsure take water sample to LFS and ask them to test for you for a second opinion, sometimes they ask a small fee but ensure you watch them do this if you can, if not, ask what test kit they use and ensure you get specific numbers of test results just not a generic āyour water is okā type of response.
Have heard of keepers getting false or wrong readings if they use dirty test tubes or using fingers over the end of tube rather than the cap when shaking the tubes, this cross-contaminates your sample and may give false/wrong results.
This is why itās worth purchasing a half decent testing kit such as API and Salifert just to name two common brands widely used in fishkeeping. And itās worth looking after your test kit, keep nice and clean and store in cool area away from direct sunlight as heat from sun or even radiators may affect the liquid solutions.
The lab based testing kit which is more accurate and are usually way too expensive to be economically viable to use for fish tanks but if you have the cash, go for it!