Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Why are you adding Epsom salt? Is the GH skewed? High Ca, low to no Mg?
Plants need both Ca and Mg. If you are correcting a low GH test simply by adding Epsom salt you are not adding the Ca that plants need.
If you need both Ca and Mg, then use a GH booster, perhaps Equilibrium. That also has K, but maybe not enough.
Other than that,
I used about the same amount of K2SO4 as I would have used of KNO3 (per EI guidelines), for some tanks that used to run high NO3 from fish food, so I did not dose KNO3 in those tanks. I used K2SO4 instead.
KH2PO4 is dosed in such low amounts it is not a significant source of K.