Water hardness test

I got some hardness test strips today to check my water. I have a 5 micron filter on my cold so I figured I'd test that first, well...... The strips only go as high as 425ppm, and I maxed it out, even with a filter. We're in a new subdivision, the house is only 1 year old, I expected to see soft water but wow. I guess I'll have to buy a finer filter. Will that help or should I just start brewing with RO water?

Any sediment filter will not remove hardness from the water. Hardness is from dissolved solids in the water mainly calcium and magnesium. An RO filter will by only allowing water molecules to pass the membrane filter in it, and a water softner will through ion exchange.