Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Probably are. Plants have plenty when the NO3 hovers between 5-20 ppm.
If it climbs much higher that may still be OK if you are running such a high tech tank that they quickly remove that much between dosing. You would not want it to drop to zero.
There is no need to add more NO3 if they are not using the NO3 that is there.
Fish seem to handle the NO3 from fertilizer better than they handle the NO3 from the nitrogen cycle. I suspect that when the NO3 comes from the breakdown of organic matter to ammonia etc. that the levels of many other things are rising, too, perhaps fish hormones or something. And it is the combination of NO3 and the other things that they do not like.