i think so. the plants (especially some floating ones) do take in nitrate, but i don't think enough to not change the water if you see it's getting close to 40ppm. My tank is pretty heavily planted now and the bacteria are eating ammonia like mad to keep up to the new bioload of ten tetra and 11 shrimp, so it's pumping out nitrates pretty hard. i did a big water change after the fishless cycle when the nitrates got to 40ppm, (ammonia and nitrites 0ppm) but even now with all the plants, the nitrates are at 20ppm what with all the fish and shrimp in a 20 gallon tank (still zero nitrites, but ammonia a little under 0.5 ppm so the bacteria are still eating like mad). I see it go past that, and I change the water 10-20% (with Prime).