NO3 and Alk consumption

[erky]

I am interested to know what is going on here. It seems that with my alk monitor I am getting a super clear view of my alk trends in my tank. I noticed that when I added 3-4ppm of nitrates (stump remover) that alk consumption went down causing my alk to spike a bit for a few days.

In the picture I have marked when I added the no3 and right off the bat there was a spike in alk, is there a correlation or am i just seeing a trend in my tank?

I have a hypothesis that my tank currently is back to under 1 ppm no3 based on what my alk is saying now (might need a few more alk tests to make sure the trend is correct) I will test no3 later today to see if I am correct or not. This brings me to suggesting that at under 1 ppm no3 my tank was growing better than with higher levels of no3. Maybe color would be better at 3-5ppm no3 and I will shoot for that in the future.

PO4 is at .05ppm (hanna ulr tester)

The two attachments show the trend for a week before adding NO3 and then after.

alk monitor is the Alkatronic.
Blue dots are when the Alkatronic turned my dosing pump off to allow the Alk to go down.

 

[Randy Holmes-Farley Verified Community Expert]

I would not assume alk consumption declined (although it is possible it went up or down), but rather the sodium nitrate addition boosts alk when the nitrate is consumed and made into tissue.

from one of my articles:


For example, if the nitrate is allowed to be converted into N2 in a sand bed, one of the products is bicarbonate, as shown in equation 2 (below) for the breakdown of glucose and nitrate under typical anoxic conditions as might happen in a deep sand bed:

1. 
   (2) 4NO3- + 5/6 C6H12O6 (glucose) + 4H2O --> 2 N2 + 7H2O + 4HCO3- + CO2
   

In equation 2 we see that exactly one bicarbonate ion is produced for each nitrate ion consumed. Consequently, the alkalinity gain is 0.8 meq/L (2.3 dKH) for every 50 ppm of nitrate consumed.

Likewise, equation 3 (below) shows the uptake of nitrate and CO2 into macroalgae to form typical organic molecules:

1. 
   (3) 122 CO2 + 122 H2O + 16 NO3- --> C106H260O106N16 + 138 O2 + 16 HCO3-
   

Again, one bicarbonate ion is produced for each nitrate ion consumed.


The addition and consumption of 50 ppm nitrate will add 0.8 meq/L (2.3 dKH) of alkalinity.

 

[erky]

I would not assume alk consumption declined (although it is possible it went up or down), but rather the sodium nitrate addition boosts alk when the nitrate is consumed and made into tissue.

from one of my articles:


For example, if the nitrate is allowed to be converted into N2 in a sand bed, one of the products is bicarbonate, as shown in equation 2 (below) for the breakdown of glucose and nitrate under typical anoxic conditions as might happen in a deep sand bed:

1. 
   (2) 4NO3- + 5/6 C6H12O6 (glucose) + 4H2O --> 2 N2 + 7H2O + 4HCO3- + CO2

In equation 2 we see that exactly one bicarbonate ion is produced for each nitrate ion consumed. Consequently, the alkalinity gain is 0.8 meq/L (2.3 dKH) for every 50 ppm of nitrate consumed.

Likewise, equation 3 (below) shows the uptake of nitrate and CO2 into macroalgae to form typical organic molecules:

1. 
   (3) 122 CO2 + 122 H2O + 16 NO3- --> C106H260O106N16 + 138 O2 + 16 HCO3-

Again, one bicarbonate ion is produced for each nitrate ion consumed.


The addition and consumption of 50 ppm nitrate will add 0.8 meq/L (2.3 dKH) of alkalinity.

Thank you for the response, how fast does that reaction take, is it almost instantly, or take time to process?

 

[Randy Holmes-Farley Verified Community Expert]

Thank you for the response, how fast does that reaction take, is it almost instantly, or take time to process?

As soon as the organisms convert the nitrate into organic tissue, or it is removed by denitrification, the alk shows up. That doesn't necessarily mean as fast as nitrate disappears from the water (since a cell taking it up but not yet using it will reduce nitrate concentration in the water but not yet release alkalinity), but I expect it happens very close in time to the nitrate declining since I don't think cells hold high concentrations of nitrate.