john6
Member
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.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?
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.
You can measure <"PO4--- reasonably easily">, but I wouldn't be too worried about <"what value you have">, plants will reduce its level. If you did want to remove phosphate from your mix and then decided that your plants were now deficient in phosphorus (P), it is <"highly mobile within the plant"> so they show pretty instant response when it becomes available again.My Phosphates are very high
There isn't a simple answer at the moment, it depends on what compound your "potassium phosphate" is.much potassium sulphate should i add to get the same amount of potassium i would get if i added potassium phosphate.
That will do.I assume you are using monopotassium phosphate (KH2PO4) as opposed to Dipotassium phosphate (K2HPO4).
1 gram of KH2PO4 will give you 5.75 ppm of Potassium (K) in 50L
1 gram of K2SO4 will give you 8.97 ppm of Potassium in 50L
5.75/8.97 = 0.64 or 64% the amount.
So , in order words, if you are currently dosing say 2 grams of KH2PO4 to reach 11.5 ppm of K in 50L you would only need to add 0.64 * 2 = 1.28 grams of K2SO4 to reach the same amount of K.
and so would that.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.
Or perhaps not as much at least... but good point, as 15 ppm NO3 with KNO3 will give you 9.5 ppm of K. I am not familiar with APFUK btw. if thats what the OP is using...Curved ball answer: if you're adding ei levels of KNO3 then you probably don't need any extra K. 🙃