I test my tanks constantly. They're on a rotational schedule so I always know the levels. The ammonia and nitrite are almost always 0ppm but the nitrate holds a steady 10-20ppm range which I remove with water changes of course. I don't have a lot of plants, mostly moss, so the nitrates don't really have a place to go. Are the Nitrosomonas and Nitrobacter really that efficient in converting ammonia into nitrite and then into nitrate respectively, or perhaps I don't have such a large load that the levels would fluctuate as I've seen in examples by other people?