# KNO3 question



## Fitos (10 Jan 2020)

I make fertilizer with KNO3. The first bag I used, my sample was always blurry.
I just opened a new one and the sample I made is crystal clear.
Which on is correct??


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## zozo (10 Jan 2020)

I'm not a professional Chemist, but how KNO3 dissolves in water is a rather light-sensitive it seems. If it's done in the dark it will be clear, is it done in the sun it will turn milky white.

And i'm not sure if i translate it correctly, i think its called liquid phase separation area. It might also be temperature related.
That's likely why labelled bottles generally say, store cool and dark. 

Could it be you mixed both in different circumstances?

I recall my first mixed batch also a tad cloudy, but i no longer premix it. Nowadays i add KNO3 in powder form directly to the tank after a water change.


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## Fitos (10 Jan 2020)

I don't remember the conditions when I did the mixtures. I never believed light and weather are so important to make a mixture. 
Actually I don't care if the mixture is cloudy or not.
I just want to be sure if my fertilizer is fine.


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## ian_m (10 Jan 2020)

KNO3 is very very very soluble in water, about 250gr will dissolve in 1 litre of water at 20'C (a huge amount, as per most nitrates) and the solution will be colourless and completely unaffected by light.

All macro EI mixes I have ever mixed up have been colourless, as expected and totally unaffected by light.

Some cheaper impure KNO3 is supplied with talcum powder added to stop it being used as an explosive pre-cursor. Talcum powder (magnesium silicate) is insoluble in water and could just be filtered out if required.

Better to but KNO3 from UKAPS know suppliers and not have any issue, as far as I am concerned.

https://www.ukaps.org/forum/threads/potassium-nitrate-kno3-purchased-from-internet.16077/


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## Oldguy (10 Jan 2020)

Fitos said:


> fertilizer with KNO3



It depends on what is blurry. Some saturated solutions look hazy as solute is coming into and out of solution resulting in differences in density and refraction. In some cases blurry/haze may be impurities. If colloidal they will remain in suspension. If of larger particle size they will settle with time or can be filtered out.





Solubility of potassium nitrate in cold water is poor. I have tried for 80g per litre but in the cold of my garage cupboard the solution has thrown very fine crystals out of solution which look like a hazy layer on the bottom of the bottle. When warmed it goes into a clear solution. In future a more dilute stock solution will be made.

For comparison sodium chloride and lead(II) nitrate are more soluble than potassium nitrate at low temperatures.

Best to buy lab or food grade pot nitrate. Food grade is easier to purchase in the UK. If bought by the 25kg sack fertilizer grade (still high purity) is about £31.55 plus VAT if collected. (Delivery costs can double the price). Still more convenient to buy by the kilo or 500g mail order. Better still have a friend who is a lab-rat, if only.

Hope that this will be of some use to you.


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