Dry ferts shelf life

swackett

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Do dry ferts have a shelf life?

We are using some we bought over 5 years ago and are still seeing some plant deficiencies even dosing ei levels, Jenner wondering if it's not as potent over time.

Ta
 

swackett

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Hi all,No you are fine <"for a while"> yet.

cheers Darrel
Interesting, our containers are not air tight and the kno3 and kh2po4 has lumps in. The mgso4 is okay.

If it has lumps is it still okay as not sure that question was answered in the the thread you posted.
 
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dw1305

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Hi all,
Should i consider buying more if its gone lumpy?
No you can just crush the lumps, or add the lumps to the tank, they are still KNO3. If you want an analogy it is the difference between granulated sugar and sugar lumps.

If you are worried about accuracy in weighing out the salts you can dry them out by heating gently. KNO3 is technically hygroscopic, but you can actually ignore the extra water (it is ~0.03% of the weight). KH2PO4 is very hygroscopic, and the lumps will contain some water. If you place it in a damp atmosphere it will eventually dissolve into a wet slurry, but when you dry it out it is back to being KH2PO4

These are soluble compounds, at 20oC you can potentially dissolve 316g of KNO3 in a litre of H2O and 222g of KH2PO4 (but not in the same litre of water).

cheers Darrel
 
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I remember one of the posts a while back when people were buying cheap kno3 off ebay with questionable contents, one of the things to look out for with kno3 is it should lump together when left. If it didn't you had to test whether it was kno3.
law of physics still applies in a sealed tupperware dish. If it's sealed the mass and elements can't change into anything else they can only be themselves or something using the same elements but in different combinations.

Oh ok, I've been helping my daughter with her physics homework :)
 

swackett

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A quick follow on question regarding this. Should I be using just normal tap water to make up my dosing mix? Been reading about people use RO/distiller water, or boiling the water etc.
 

dw1305

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Hi all,
A quick follow on question regarding this. Should I be using just normal tap water to make up my dosing mix? Been reading about people use RO/distiller water, or boiling the water etc.
RO or DI water would be best, but it isn't essential. You may find that you have precipitation with tap water, or possibly some of the salts coming out of solution if you make up a really strong mix (via the common ion effect).

If you have a precipitate you could add an acid (white vinegar would do) to the stock solution and you may find that the salts go back into solution.

Boiling the water will remove temporary/permanent hardness, but not anything else. If you boil the water you need to strain it into jug etc. immediately. Otherwise as the water cools any solid CaCO3 ("limescale") will go back into solution, via the carbonate ~ CO2 equilibrium.

If I didn't have an easy to obtain source of RO/DI water, I'd use rain or boiled water.

cheers Darrel
 

swackett

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Per
Hi all, RO or DI water would be best, but it isn't essential. You may find that you have precipitation with tap water, or possibly some of the salts coming out of solution if you make up a really strong mix (via the common ion effect).

If you have a precipitate you could add an acid (white vinegar would do) to the stock solution and you may find that the salts go back into solution.

Boiling the water will remove temporary/permanent hardness, but not anything else. If you boil the water you need to strain it into jug etc. immediately. Otherwise as the water cools any solid CaCO3 ("limescale") will go back into solution, via the carbonate ~ CO2 equilibrium.

If I didn't have an easy to obtain source of RO/DI water, I'd use rain or boiled water.

cheers Darrel
Perfect thanks Darrel, we have some precipitation with our solution. If boiling then what would I strain it with (how fine should the strainer be)?

thanks again
 

dw1305

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Hi all,
we have some precipitation with our solution
Try a dash of white vinegar, if the precipitate doesn't go back into solution you could try warming the solution (the solution with the vinegar is fine). If neither of those work then you will need to throw that one away.
If boiling then what would I strain it with (how fine should the strainer be)?
It just needs to remove the fine particles of CaCO3 from the water.

I must admit when I've done it I haven't bothered too much and I've just poured the boiling water through an old fashioned tea strainer. Something like a cotton handkerchief, or a brine shrimp net, would be more efficient in removing finer particles.

cheers Darrel
 

swackett

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Thanks just got 2.5L of de-ionised water from Sainsbury for £1, remixed and within hour all mixed in with no settlement.

Thanks Darrel.
 
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