So I wanted to get an idea of what ammonia is in my aquarium. 20 litre nano cube. I took a reading before a water change that I did today. It was 0.1 mg/l which I expected since I added some fish this week. Top end of the scale according to the JBL test kit. Then I took a reading after a 50% or more water change. And the reading was higher! 0.6-1. I did the test 3 times and it was higher. I did a reading on the water that I used for the change, a cut of 50:50 tap to RO. That was zero. Of course! Can anybody explain please?? What the heck is going on??