The marine kits are meant for accuracy in seawater. Unless you have a freshwater kit.Well, I believe my ammonia is truly at .25 because I decided to test some water straight out of a jug of purified water to see what color it would be and it was as yellow as the yellow on the card. It was just as yellow as my nitrates usually look. I think this would be a good test for anyone to do that is wondering if their api test are accurate or not.