Kno3 Potassium Nitrate

The x-y-z you see on bottles usually refers to N-P-K-Fe-trace concentration in %.

So for pure KNO3 you will have 14-0-39. But in the hobby most people report N as NO3 which is 61%.

Watch out, most terrestrial fertilizers also use NH4NO3 urea and others. Depending on local regulations this may be detailed or not.

 

No problem. I will go step by step and by the end of it you will be able to calculate the N % from the other molecules on your own.

To simplify things a little, every chemical element has an average atomic mass. When the elements join together they form a molecule with an mass equal to the sum of the elements.

In order to work with common units of mass we use a lot of molecules 6.022*10^23, which represents a mole. Put simply a mole is a unit that tells you the number of things, no need to concern yourself anymore with it at this stage. Just defining it as it will come up later.


From chemistry we know the average atomic weight of all the elements (easy to find out, Wikipedia, Google, etc).

Let's work trough an example:

Element - - - Atomic weight(g/mol)
K---39.1
N---14
O---16

To find the molar mass of KNO3 make the sum of the components.
K*1+N*1+O*3=
39.1+14+16*3=
39.1+14+48=
101.1 g/mol

We want to find out what percentage of KNO3 is N.

N/KNO3*100=14/101.1*100=13.8

So in 100g KNO3 you have 13.8g N

What about NO3?
NO3/KNO3 *100=
(14+3*16)/101.1*100=
62/101.1*100=
61.3

So in 100g KNO3 you have 61.3g NO3

Now, a few observations :
1. Obviously you cannot measure NO3 alone. You weight the substance(KNO3) and produce the theoretical weight of each ion.
2. There are certain rules that dictate what happens when/if a molecule is dissolved in water. For example KNO3 will separate into K+ and NO3-. There will be no free O or N because water. Is not strong enough to break them apart.
3. Still we know plants take up NO3 directly and are able to use the N from NO3 so it is not wrong to calculate the N conc.

 

You also asked about using something other than KNO3... You sure can do it but. You have to be a lot more careful. Urea is not the only replacement, NH4NO3, NH3 also work.
Just be sure to have low pH values when dosing, <6.5, break the dose into daily, 2x 3x per day.

The problem with them(also urea) is that they are toxic to fish, shrimps and plants in high enough conc. And the toxic level is quite low. When the bio filter is mature it should quickly process these substances into NO3, making them safer. You can experiment and see how much how fast the filter is able to remove NH3 and NO2 from the water.

Another option would be to run a parallel tank where you enrich water with NH3 and give it time to be converted to NO3. Then simply use that water to fertilize.

Before you give up on NO3, also look at hydroponics shops, meat conservation shops, general chemical providers. You might also find a farmer who is willing to order some for you. It all depends on the regulations in your country, some countries love to require a license to buy a hammer or a screwdriver, because you can hurt or kill a man with it. Oh well, always respect the laws of your country of residence.

 

Hmm, this post must have slipped through. Thanks to Julia Adkins it was brought back to my attention.

Pure KNO3 would be N-P-K : 13.8-0-38.6 . The 4 component is likely to be S or Mg. Since there seems to be more K I would think that there was some K2SO4 added to the mix. Perhaps the answer lies in the Chinese writing. Also look for the purity of the product, you would like something with more than 90% purity. All KNO3 is water soluble at room temperature up to a point so with a typical solution you do not need to worry.

I would also check if the product is genuine. Make your fertilizer and dilute a small amount to get something like 10 or 20mg/L, something that is easily distinguishable on a NO3 test kit. There have been cases where powders got mixed or the seller was not genuine.

Hi @Julia Adkins. I hope I understand your question correctly, if not let me know.

Every chemical element has its average atomic weight. This can be found in most chemical tables. Based on this atomic weight we can calculate the mass of a mole of substance in g. As the weight % remains the same independent of the actual number of moles of substance we can apply the percent to every mass of the same substance.

How does this look in practice ?

K- Atomic weight: 39.1
N- Atomic weight: 14
O- Atomic weight: 16

Molar mass of KNO3 is calculated by adding up all the atomic weights multiplied by the number of atoms existing in a molecule.

39.1*1+14*1+16*3=101.1 g/mol

We can then calculate the mass percent as described above:

For N for example: 14/101.1*100~=13.85% N

Another example for O : 16*3/101.1*100~=47.47% O

Add them up and you will get:
47.47+13.85~=61.33 % NO3 in KNO3

I am afraid I cannot give you a reference but any good university level chemistry compendium should have a sub-chapter on this calculation and these formulas. If you do not find one, PM me and I will search for one. As you see it is mainly math.

The 14.5% nitrates mentioned in your post seem more like the percentage for N (nitrogen), not NO3 (nitrates). Indeed this seems to be the case as on the website you mention under "Potassium Nitrate" there is : "13.5-0-46.2". I assume this is N-P-K. The 13.5% N might just be a rounding error , or adjusting for the (im)purity of the product. The K is way too high. Unless you add an extra source of K, the 46.2% is typo.

Most people target 20mg/L nitrate (again NO3) which is about 4.5mg/L nitrogen (N). Many countries have very specific bans on many -NO3 compounds. Check with your specific country legislation regarding importing such chemicals. Urea is another source of N, though less safe to use regarding algae and fish.