Would KH2PO4 meant for use with terrestrial plants in agriculture be safe to use in dry ferts?

[MotaBhai]

No one here sells salts for aquarium use specifically and I've only been able to find Monopotassium phosphate for use in agriculture/terrestrial crops. Will it be okay to use it or would there be problems due factors such such as purity? This is the most commonly available option here: Monopotassium Phosphate Fertilizers - Haifa Group

I apologize if this isn't the right place to ask this question, this is my first time interacting with the forums.

 

[Simon Cole]

That Haifa product you have linked looks ideal.
It states: "Free of chloride, sodium and other detrimental elements"
This is the right thread. If you need any more help please ask. Welcome to UKAPS.

 

[Zeus.]

Like posted above it sounds like a suitable product for our/your needs


Just bear in mind you will also be adding K (potassium) as well. On hols ATM but I will add it to the IFC calculator which will do the maths and give the yields for P and K for a given dose - unless some else else does the maths before hand 😉

 

[dw1305]

Hi all,

unless some else else does the maths before hand ........

Easy enough, because the calculations are already here: <"percentage for dry fertilizers">

To convert P2O5 to P you multiply by 0.436.

So 52 x 0.436 = 22.7% phosphorus (P).

If you want to know how much PO4--- that is, it is bit more complicated because you need to know the percentage of P in P2O5 (43.7) and the percentage of P in PO4 (32.6), the divide 43.7/32.6 = 1.34, so 10 mg/L P2O5 = 13.4 mg/L PO4, to go the other way around PO4 to P2O5 its 32.6/43.7 to give you multiply by 0.747.

So if you want that as the phosphate ion (PO4---)? 69.7% PO4---

Potassium (K) from potassium oxide (K2O) is fairly straight forward, just multiply the K2O value by 0.83 to give you mg / L (ppm) K.

and 34% K2O = 28.2% potassium (K)

for a given dose

This would be 2g KH2PO4 dosed in 100 litres (via <"Nutrient Dosing Calculator">).

PO4	13.96 mg / l (ppm)
P	4.55 mg / l
K	5.75 mg / l

and a check:
P: 13.96 / 4.55 = 3.07 and 69.7% / 22.7% = 3.07
P : K 4.55 / 5.75 = 0.79 and 22.7% / 28.2% = 0.80

cheers Darrel

 

[Zeus.]

unless some else else does the maths before hand 😉

@dw1305 Well you did come to mind 🙂
A double check also helps.
Found some time - had an easy back door to the IFC so didn't take long
Used the same dose ratio as Darrel via the DIY Calculator in the IFC and made a 500ml solution and added 500ml to a 100l tank or just dry dosed 2g in 100litres and compared it KH2PO4

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So based on mine and Darrels results you can treat the Haifia MPK as if you was adding KH2PO4 in any fert calculator and you will be fine. If you choose to used the IFC calculator just use the mass it gives for KH2PO4 for the mass of Haifia MPK as for our purposes they are the same IMO (I did repeat myself just to be clear )
It doesn't show the solubility limit for Haifia MPK as I assumed it was a soluble as KH2PO4 or of a very similar solubility