The magnesium/calcium nitrates reminds me of the older German formulas If I remember correctly. Also reminds me of Tobi's mix. Those Germans love their nitrates.
I've been reading a plant physiology book for fun and its saying something about the negative NO3 ions and positive NH4+ balancing the pH intracellulary (remember compartmentalization results in different pH values). Maybe that's the reason it works? Though the book is mainly about terrestrial plant. Just some preliminary thoughts, nothing conclusive.