Got,

As others have pointed out it is easy to get your water tested for
hardness. If you don't want to buy the kit take a glass jar of cold tap
water to Sears, stand near the water softeners, look prosperous. A salesman
will show up quickly to test your water.
It's possible that your hot water tank is a reservoir of hardness. After
3 months I would be surprised though but drain and refill it.
I own a Sears unit. It works ok but the rotary valve needs to be cleaned
annually and the price of Sears parts is scandalous.

Dave M.