I recently bought my first API test kit (I had been doing weekly tests at my LFS to do fishless cycles) and after testing the water in all three of my established and heavily planted tanks, ammonia was .25 ppm and nitrites/nitrates were zero. How is this possible? After some digging, I found many claim that the ammonia reading is a mistake (which would make sense, as my reading was zero before I added fish). Is this true or is there any way I can correct this? Also, is there any reason to perform weekly water changes (aside from gravel/detritus cleaning) when nitrates are 0?