Your water is quite hard, but I don't think this is a problem. I don't think using the softened water would help or hurt necessarily.
As I understand it potassium is generally not tested for. I just dose my water I'm changing anyway.
You should be able to buy a phosphate test kit at any good fish store, If you are dosing phosphate it is a necessity.
What fertalizers are you using? You should at least give it a little Flourish every week or so. Your plants will starve if you don't give them the nutrients they need.