Likely better to say:
Inorganic N forms: N2 gas, NH4+, NO3-, NO2- etc
Organic forms: Glutamine, Glycine, enzymes etc
This may help put it more into prespective:
http://www.norganics.com/nitrogen.pdf
However, realize that we add plenty of Carbon from CO2 that's fixed into active growing plant tissue.
Reduced carbon.........
That's fine if the plant tissue is healthy and growing well.
But bad if not, as bacteria will consume the tissue and give off lots of CO2 in the process as well as cellular contents that also leak out into the water.
Total nitrogen - Plant Management in Florida Waters
When plant tissue dies, it leaches and decays various forms of N.
This is dependent on the species, the temperature, O2, concentration of decaying material and it's ratio of C:N.
While a tank might be fine, if the plants suddenly stopped growing an decayed some, this would change the O2 and alter the system radically.
Regards,
Tom Barr