You should be good with:
KNO3 - macro nutrient
KH2PO4 - macro nutrient
K2SO4 - used for extra K; also used to add hardness
MgSO4 (Epsom Salt) - used for extra Mg; also used to add hardness
CaSO4 - used for extra Ca, also used to add hardness
It would be helpful if you had micro nutrients as well.