# Dry Fertilizer Identification Help



## trag (Jan 9, 2008)

I bought two pounds of K2SO4 from aquariumfertilizer.com. And they're both labeled K2SO4. However, one is a fluffy powder. The other is more like a bag of salt crystals. Is K2SO4 fluffy or crystally? Or either one depending on grinding or drying method? 

The bag of KH2PO4 I bought says on the label after the mixing instructions, "The result will be a 0.3% P2SO4 solution". Which implies that the contents of that bag are actually P2SO4 rather than MKP (KH2PO4) even though the bag is labeled as "Mono Potassium Phosphate - 0-51-34" in large letters.

Boy this is not inspiring confidence.

So is the K2SO4 a fluffy powder or a crystally substance? If it can't be both, then what is the other one?

And is my MKP really MKP? Which is correct? The portion of the label which says it is MKP, or the mixing instructions which seem to say it is P2SO4?

And can I trust that the CaSO4 I received, which is also a fluffy powder is actually CaSO4 and not K2SO4? Or vice versa?

Am I dosing what I think I'm dosing?

The folks at aquariumfertilizer.com shipped my stuff really fast. And when they left an item out they sent it along cheerfully when I pointed out the error. However, their labeling is not inspiring confidence here.

Anyway, I'd appreciate any physical descriptions of the dry ferts listed (K2SO4, KH2PO4 (MKP), P2SO4, and CaSO4.


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## Aquaticz (May 22, 2009)

They are quite reputable. I know what you mean about the 
K2S04 being fluffy or crystalized. I ordered a buch and noted the same thing. I used both and they are fine. The only problem with the fluffy stuff is that it tends to form what one would call a clod or rock which makes it a little harder to measure or weigh. I just crushed it & have had no problems.
HTH


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## trag (Jan 9, 2008)

Aquaticz said:


> They are quite reputable. I know what you mean about the
> K2S04 being fluffy or crystalized. I ordered a buch and noted the same thing. I used both and they are fine. The only problem with the fluffy stuff is that it tends to form what one would call a clod or rock which makes it a little harder to measure or weigh. I just crushed it & have had no problems.
> HTH


Ah, thank you. That is a relief. I tasted a dab of both K2SO4 samples on my finger, and they didn't seem to taste quite the same, which worried me, as my built-in chemical test system should identify them the same... The crystally stuff had a slightly more salty (but not quite like NaCl) taste to it. I also tasted the CaSO4 and it had quite a different flavor with a bit of a metallic alkali flavor which was encouraging.

I'm going to mix of a sample of both K2SO4 batches and test them for nitrates (KNO3) and phosphates (KH2PO4) just to be certain. I wish I had a potassium test... On the other hand, even if it is one of the above two, that would still contain potassium, I'd just be getting more of another macro than I expect.


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## trag (Jan 9, 2008)

I calibrated my API nitrate test kit this weekend (will post another thread on that). After calibration, I tested my two K2SO4 powders for nitrates.

Because I only cared (at this point) whether nitrates were present, I mixed 1g of K2SO4 with 100 ml of water. This would produce a highly concentrated solution.

The crystally K2SO4 reads between 5 and 10 ppm of nitrates. 

The fluffy powdering K2SO4 reads zero (0) nitrates. The test solution stays yellow after five minutes (yes, I shook the second bottle).

My distilled water reads zero (0) nitrates.

It was unlikely (careful rinsing) but conceivable that my test of the crystally powder was contaminated by my previous testing of nitrate solutions, so I cleaned everything and ran the crystally test again, after testing the powdering K2SO4 and after testing my distilled water. So not only was everything carefully cleaned, but two previous tests with the same equipment and procedures showed zero nitrates.

The second crystally K2SO4 test showed the same results as the first.

So, it would appear that the difference between the powdery K2SO4 and the crystally K2SO4 is that the latter has a small amount of impurity, probably in the form of KNO3. I can't see where this would cause any issues. Given the high concentration of solute, and the low ppm reading of nitrate, the contamination/impurity must be pretty tiny. Perhaps something like one part in 500 of the powder is KNO3 instead of K2SO4.

I have not yet tested for phosphates. Ran out of time to do the calibration and all the other stuff.


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