# Need help with calculation



## grshs_vny (Sep 4, 2010)

Hi,i need some help to calculate nitrate concentration in one gram of potassium nitrate.please reply ASAP.


----------



## HeyPK (Jan 23, 2004)

The atomic weights : K=39, N=14, O=16
The molecular weight of KNO3 is 39+14+(3 x 16) = 101. 
The molecular weight of NO3 is 14+(3 x 10) = 62
62/101 = 61.4. So potassium nitrate is 61.4% nitrate
1 gram of KNO3 would contain 0.614 g of nitrate or 614 milligrams of nitrate.


----------



## grshs_vny (Sep 4, 2010)

HeyPK said:


> The atomic weights : K=39, N=14, O=16
> The molecular weight of KNO3 is 39+14+(3 x 16) = 101.
> The molecular weight of NO3 is 14+(3 x 10) = 62
> 62/101 = 61.4. So potassium nitrate is 61.4% nitrate
> 1 gram of KNO3 would contain 0.614 g of nitrate or 614 milligrams of nitrate.


thanks HeyPK for quick reply.


----------



## grshs_vny (Sep 4, 2010)

Hi,HeyPK can you explain how adding 2ml of standard solution made by mixing 20g of KNO3 in 500ml of water adds 5ppm NO3 to 10liters water?because my calculation is giving different value
20grm of KNO3 contains 7.6grms of NO3 means 500ml contains 7600 miligrams of NO3,so each ml contains 15.2mg


----------



## grshs_vny (Sep 4, 2010)

grshs_vny said:


> Hi,HeyPK can you explain how adding 2ml of standard solution made by mixing 20g of KNO3 in 500ml of water adds 5ppm NO3 to 10liters water?because my calculation is giving different value
> 20grm of KNO3 contains 7.6grms of NO3 means 500ml contains 7600 miligrams of NO3,so each ml contains 15.2mg


sorry i got my answer 20 grms of KNO3 contains12.4 grms of NO3 not 7.6 .I got confused it with potassium .thnks anyway


----------



## grshs_vny (Sep 4, 2010)

grshs_vny said:


> Hi,HeyPK can you explain how adding 2ml of standard solution made by mixing 20g of KNO3 in 500ml of water adds 5ppm NO3 to 10liters water?because my calculation is giving different value
> 20grm of KNO3 contains 7.6grms of NO3 means 500ml contains 7600 miligrams of NO3,so each ml contains 15.2mg


Sorry i got my answer 20 grms of KNO3 contains12.4 grms of NO3 not 7.6 .I got confused it with potassium.Thanks anyway.


----------



## grshs_vny (Sep 4, 2010)

*ReOTASSIUM NITRATE*

From this calculation it is observed that adding potassium nitrate to supplement potassium increases nitrate concentration dramatically.
In case of 200Ltrs tank target value for potassium in water column is 20 ppm so 10grams of KNO3 is required,This also increases nitrate to nealy30 ppm,which is not good for plants(required target)5-10ppm.
Therefore it is better to use 2 or more compounds to add potassium


----------



## Seattle_Aquarist (Mar 7, 2008)

Hi grshs_vny,

Correct, most of us add Potassium Sulfate (K2SO4) if all we want to increase is the Potassium.


----------



## ray-the-pilot (May 14, 2008)

Seattle_Aquarist said:


> Hi grshs_vny,
> 
> Correct, most of us add Potassium Sulfate (K2SO4) if all we want to increase is the Potassium.


But that also increases sulfate. What is the correct level for sulfate?


----------



## HeyPK (Jan 23, 2004)

20 grams KNO3 x .614 = 12.8 g of NO3
12.8g/500 ml x 2 ml = .04912 g in 2 ml or 49.12 milligrams in 2 ml of the standard solution. 

You put 2 ml of the standard solution in 10 L of water
49.12mg/10L = 4.912 mg per liter. 
milligrams per liter is the same as parts per million because a liter has 1 million milligrams

So, the final concentration is 4.9 ppm (almost 5).


----------



## grshs_vny (Sep 4, 2010)

ray-the-pilot said:


> But that also increases sulfate. What is the correct level for sulfate?


Even I have the same question.


----------



## Diana K (Dec 20, 2007)

From Diana Walstad's book, charts on pages 78, 80 and 83:
Plants seem to use sulfur at about the same rate as magnesium, about 1/3 as much as calcium, about 1/2 as much as phosphorus, or 1/10 as much as potassium. 

On the other hand, I do not see problems when I am dosing K2SO4 for potassium. 

I would indeed way overdose on phosphate and nitrate if I used these as a source of potassium. At the low levels I am currently dosing of KNO3 and KH2PO4 I can keep the nitrate between 5-10 ppm (mostly from fish food, though) and the phosphate between 1-5 ppm. I sure do not want to dose more of these.


----------

