I was reading through some of the articles including the one titled "How ammonia is converted to nitrate"
and saw an error that you may want to correct. Near the end of the article, it says that "Nitrate is safe for fish but not for corals."
The fact is that not only are nitrates not safe for fish, but can be lethal in sufficient concentrations. It is more accurate to say that nitrates are less
toxic than ammonia or nitrites. If memory serves, I think in a FO
tank, you still want nitrates to remain under 20 ppm
. Higher nitrates, while not necessarily fatal, will hinder growth and overall immune response.