Once again RHF delves into the grind, brilliant article
Nitrate in the Reef Aquarium - REEFEDITION
Nitrate in the Reef Aquarium - REEFEDITION
Most of the nitrate present in the ocean results from the recycling of organic materials. The degradation of plankton, for example, provides nitrate. This can be shown in a simplified chemical equation describing what happens when organic “food” is digested with oxygen:
(CH2O)106(NH3)16(H3PO4) + 138 O2 → 106 CO2 + 122 H2O + 19 H+ + PO43- + 16 NO3-
which in words reads as:
plankton + oxygen → carbon dioxide + water + hydrogen ion + phosphate + nitrate
Note that this process consumes alkalinity (the H+ being produced shows this). So when nitrate is accumulating in a reef tank, alkalinity is being depleted. Production of 10 ppm of nitrate will deplete about 0.16 meq/L (0.45 dKH) of alkalinity. If this nitrate is removed by water change, that alkalinity is lost forever. If the nitrate is taken up by an organism (algae, coral, bacteria, etc.) and used, then all of that alkalinity is returned to the system (see equations below showing this fact).