In a tank with no live plants, increasing nitrate shows that the second stage of cycling is underway. However, plants change the process of cycling. If there are enough plants to take up all the ammonia made by the fish, there would be no reading for ammonia - or nitrite or nitrate as plants turn ammonia into protein rather than nitrite. Bacteria will grow slowly but not nearly as many as in a tank with no live plants. In a tank with live plants, but not quite enough of them to deal with the ammonia made by the fish, the left over ammonia will be turned into nitrite then nitrate.
Whenever there are fish in a tank, if there is a reading for ammonia or nitrite, water changes need to be done.
Excellent explanation. Thanks!
Really getting good exercise with all these water changes