Adding Nitrates Raises Alkalinity?

Trevor40 · May 25, 2018

I have been dosing Potassium Nitrate(Stump Remover)for a few days and noticed that my Alk raised a little bit in my sps tank even with not dosing Alk to the tank.

Randy Holmes-Farley · May 25, 2018

Yes, when the nitrate is metabolized, it adds alkalinity:

for example, in photosynthetic organisms:

122 CO2 + 122 H2O + 16 NO3- --> C106H260O106N16 + 138 O2 + 16 HCO3-

or in denitrification;

4NO3- + 5/6 C6H12O6 (glucose) + 4H2O --> 2 N2 + 7H2O + 4HCO3- + CO2

In either case, you get about 2.3 dKH for every 50 ppm of nitrate consumed.

Trevor40 · May 25, 2018

Interesting and thank you for the response. I wonder if this is part of the reason to add Nitrates slow to avoid alkalinity fluctuation or would the change be so small that it barely matters?

Would this be one of the reasons a new tank has a hard time keeping SPS because nitrate metabolism fluctuates in a new tank?

GoVols · May 26, 2018

@Trevor40
Great thread!! ;Woot

Randy,
Thanks for always helping us understand.... ;Writing

Randy Holmes-Farley · May 26, 2018

Trevor40 said:
Interesting and thank you for the response. I wonder if this is part of the reason to add Nitrates slow to avoid alkalinity fluctuation or would the change be so small that it barely matters?

Would this be one of the reasons a new tank has a hard time keeping SPS because nitrate metabolism fluctuates in a new tank?

Most people add little enough nitrate (say, 5 ppm) that the effect is quite small in terms of fluctuations in alk (0.2 dKH over however long it takes that nitrate to be consumed). .