The basic fact is that plants prefer ammonia to nitrates, so in theory, if his anoxic filter is working 100%, all his plant growth is solely due to ammonia as a source of nitrogen.
It is "the basic fact" that plant uptake of NO3 is higher when a little ammonia is present. So total N uptake will be even greater when NO3 and NH4 are present. Any number of aquatic plant studies will show this. NO3, not NH4 is the standard in normal, unpolluted waters. Plants are adapted to perform better when NO3 is present. I do not understand this fascination with removing NO3 from systems...
I'm always a little wary of situations where people use Dr. in their title (except for Dr. Pepper). ... What you need to do is deplete the oxygen in the system as fast as possible to generate anoxic zones, so you would never leave it open to atmosphere. What he doesn't seem to mention is what happens to the nitrates in the system. There are really two paths that it could take, first it could be converted back into ammonia which his test strips convenient don't test but would explain his decent plant growth. Second it can be converted to nitrite --> nitric oxide --> nitrous oxide --> nitrogen (gas). But the absence of bubbles in his system makes me think that he's just converting stuff back and forth.
100% correct Prof. Dr. Dr. JusticeBeaver. I hear all fish prefer a good jug of NO2 over NO3 every day.