Calcium/Potassium/Sodium nitrate

Myka · Aug 2, 2015

To help figure out which chemical I want to use to dose nitrate in my tank I'm (trying) to do the maths. Can someone please confirm, and then this information will be available all in one place for others to use too. I have a bag of potassium nitrate and I'm curious how much it will affect potassium which is what spurred this thought process...

1 ppm N = 19.9 ppm NO3

Potassium nitrate KNO3
13.9% nitrogen
38.7% potassium
For every 1 ppm potassium you get 0.36 ppm nitrogen or 7.1 ppm NO3.

Calcium nitrate anhydrous Ca(NO3)2
45% nitrogen
55% calcium
For every 1 ppm calcium you get 0.82 ppm nitrogen or 16.32 ppm NO3.

Sodium nitrate Na(NO3)
??

Randy Holmes-Farley · Aug 3, 2015

The calcium data is off.

Calcium nitrate is 76% nitrate and 24% calcium. So 1 ppm calcium boosts nitrate by 3.1 ppm.
Sodium nitrate (NaNO3) is 27% sodium and 73% nitrate. So 1 ppm sodium boosts nitrate by 2.7 ppm.

For most situations, the boost to K, Ca, or Na is too small to worry about.

Myka · Aug 3, 2015

Randy Holmes-Farley said:
The calcium data is off.

Calcium nitrate is 76% nitrate and 24% calcium. So 1 ppm calcium boosts nitrate by 3.1 ppm.
Sodium nitrate (NaNO3) is 27% sodium and 73% nitrate. So 1 ppm sodium boosts nitrate by 2.7 ppm.

Thank you Randy.

Is your data for Ca(NO3)2 anhydrous? (or tetrahydrate?) Or is the difference negligible anyway?

By my research, it appears Potassium nitrate is only about 53% potassium and nitrate, what's the other 47%?

Randy Holmes-Farley said:
For most situations, the boost to K, Ca, or Na is too small to worry about.

From past experiences this seemed to be the case, now I see the data.

Tonight I will work on making up some recipes for solutions using these chemicals and add this information to this thread.

Randy Holmes-Farley · Aug 3, 2015

For the relation between the metal and the nitrate (e.g., X ppm K+ for Y ppm Nitrate), it doesn't matter if it is anhydrous or not, although the weight of solid you need to dose to get to a particular boost will vary. The % I quote are anhydrous.

Potassium nitrate itself is typically anhydrous, and the online sales sites I see show 98-100%. If you find some where K and nitrate don't add up to close to 100%, it may be due to inert things added such as in a fertilizer to help disperse it.

Myka · Aug 3, 2015

Ok thank you Randy. I got my numbers from a planted aquarium fertilizer website. Essentially, as long as we use a product that's as close to 100% pure as possible it really doesn't matter which compound we use because the bulk of the chemical will be nitrogen. Good to know.

Randy Holmes-Farley · Aug 3, 2015

You're welcome.

Happy Reefing!

Myka · Mar 24, 2016

Revisiting this Randy (I think Jim could probably figure this out too hehe)...

I'm trying to figure out how much nitrate in ppm I am dosing per day. I am using Sodium nitrate. It is lab grade, 99.5% purity minimum. The molecular mass is 84.99467 g/mol. I believe NaNO3 is about 39% nitrogen by weight... so 33.15 g/mol?

My solution is 30 grams NaNO3 added to enough water to make exactly 500 mL solution. I'm adding 10 mL solution to about 80 gallons or 302,833 mL of water (I measured rock/sand/glass displacement - this number is probably accurate within a couple gallons). If I have 30,000 mg in a 0.5 L solution, the solution is 60,000 mg/L. Of that 60,000 mg/L 39% is nitrogen or 23,400 mg/L nitrogen or 465,660 mg/L nitrate. I am adding 1/50th of the solution or 9313 mg/L nitrate. I am diluting it from 10 mL into 302,833 mL...and now I am lost if I have not already gone off in the wrong direction.

Using this calculator, I think I came to the answer of 2.988 mg/L or just under 3 ppm nitrogen or about 60 ppm nitrate. My test kits (Salifert & Red Sea Pro) are telling me I'm adding about 0.25 ppm.

I want to know the maths. Please help. I'm so lost...

Randy Holmes-Farley · Mar 24, 2016

Sodium nitrate has a molecular weight of 85 g/mole. Nitrate is 62 g/mole.

So sodium nitrate is 73% nitrate by weight.

If you add 30 g of sodium nitrate, that is 21.9 grams of nitrate per 500 mL, or 44 mg/mL

Adding 10 mL to the tank adds 440 mg.

Added to 303 liters (your tank volume), the addition is 440 mg/303 L = ~1.5 mg/L.

Myka · Mar 24, 2016

Thank you Randy! Now I can figure this out myself in the future.

I knew there was an easy answer, and I thought of going that direction, but for some reason I talked myself out of it. Now I have to go shake my fist at my test kits!

(although 0.25 ppm compared to 0.75 ppm for a hobby grade test kit actually isn't too bad at all)