My Phosphates are very high so i am stopping mixing potassium phosphate in my dry mix, how much potassium sulphate do i need to add to 500ml water to get the same amount of potassium i would get using potassium phosphate?
It would depend on which "potassium phosphate" salt you are using, unfortunately there are two options. Dipotassium phosphate (K2HPO4.xH2O) contains more potassium than monopotassium hydrogen phosphate (KH2PO4). There is a further complication in that dipotassium phosphate can have various numbers of "xH2O" <"water of crystallization"> attached.
Potassium sulphate (K2SO4) is a bit more straight forward. It has a Relative Molecular Mass (RMM) of 174.3 and potassium has a RAM of 39.1. The potassium percentage then becomes (39.1 * 2)/174.3 = 45% K
Because it has less "unknowns" I'll use KH2PO4, which is 28% potassium. The difference between them, in potassium content, would mean that 10g of monopotassium hydrogen phosphate (KH2PO4) would be equivalent to 6.22g of potassium sulphate (K2SO4).
I dont think i was specific enough.
I dont want to add Phosphate at the moment.
I use the dry ferts you get with the starter kit from APFUK and use their recipe for EI dosing, One of the salts is Potassium phosphate but i dont want any phosphates adding, so i got some potassium sulphate so how much potassium sulphate should i add to get the same amount of potassium i would get if i added potassium phosphate.
Hope this makes sense
One of the salts is Potassium phosphate but i dont want any phosphates adding, so i got some potassium sulphate so how much potassium sulphate should i add to get the same amount of potassium i would get if i added potassium phosphate.
Further to Michael’s post above, to relate that to your APFUK 500ml bottle and their dosing recipe - instead of the 1 tsp (6g) of KH2PO4, you would add around 2/3 tsp (4g) K2SO4. To be honest though, the APFUK recipe is a little light on K, so I would just add a whole teaspoon.