I use the API master test kit. Fish are all fine which is why I wondered about false readings. Makes no sense to me. It's a 75 gallon freshwater. I have 7 mollies 2 small angels, 3 platys, 3 phantom tetras, 4 neons, 2 serpae tetras, 1 pleco. It's been set up about 7 weeks. I went to lfs yesterday & got prime & a filter media that's supposed to reduce ammonia & some plants. I added that last night. The media went in only one filter that had only carbon filter in it so did NOT remove the old filters. I plan to do another water change today if tests high again when I get home.