kH has nothing to do with the hardness of your water. It is related to the total alkalinity. Things that add alkalinity like PO4-3, HCO3-, CO3-2,or OH- will increase kH.Im sorta confused here and don't know how to fix this. I have always had soft water with a kh of 120 ppm now its sayin my water is very hard and the kh is 300+
The white streaks in the rocks look like marble which is CaCO3. This will increase both GH and kH.Those could be limestone rocks. If so, they will increase both the KH and the GH as they very slowly dissolve in the water. They are probably a mix of calcium carbonate (limestone) with some magnesium carbonate mixed in.