thats what i mean, you should definitely be seeing ammonia if you have been putting 5 flakes of food in your water for five days, and in only a 20L tank. your ammonia tests should be positively showing ammonia at some number between 1-5 i would have thought. if your tank was producing enough nitrosoma/nitrobacter bacteria to drop this to nli, then you would have a reading for nitrites, yet you state this is nil. very strange. thats why i asked if it is distilled water. it's almost as though your water is too pure for anything to live in it. i'm stumped