My ammonia level seems to be not going below 0.25 ppm since 1 week even after water change and increasing the media (ceramic rings). The nitrites are 0 and nitrates are 10-20 ppm. It's a well planted 20 gallon long tank (water sprite, anubias, hornworts and crypts). The plants grow crazy as well as fish are doing good too (3 panda cory and 1 dwarf puffer). Any reasons you think of that can be causing this ammonia. Also, I use flourish root tabs and nilocg 2 squirts in a week.