Agree. In a tank with fish, nitrates should be kept as close to zero as you can. If you have no fish and just plants, it is solely a matter of providing adequate balanced nutrients of which nitrogen is one.
Freshwater fish are impacted by nitrates; the extent they are depends upon the species, the level of nitrates, and the length of exposure time. There are no tropical fish habitats that have nitrates anywhere close to what we have in aquaria (except for those who do maintain zero nitrates). My tanks have tested in the 0 to 5 ppm range for more than a decade; for all I know nitrates might be zero. I have fish and plants. A stable biological system in an aquarium is one in which the nitrates never increase from one water change to the next; keeping them as low as possible, and consistently at that level, is the goal.
Except in high-tech method planted tanks, there is no reason to add nitrogen/nitrates to an aquarium as in plant fertilizers. Most of us have low-tech or natural method planted tanks, where we have fish (maybe too many almost) and consider plants as aesthetical and beneficial because they help maintain clean water. The plants in these tanks do not take up nitrate except as a last resort; they prefer ammonia/ammonium as their source of nitrogen, which is why they are so beneficial. Floating plants which grow rapidly are often termed "ammonia sinks" for this reason--they can assimilate more ammonia than the fish and organic decomposition is likely to provide. But so long as ammonia is available, and if the other 16 nutrients are sufficient, and the light is sufficient, the plants will take up ammonia/ammonium exclusively.
