Samsung fridge: Hard water even after changing water filter

The refrigerator water filter is trying to remove some dust, contamination, and possibly chemicals. So if your tap water is having low contamination then filter won’t improve the PPM level. We live in Austin, TX where tap water has 165 ppm level. With refrigerator filter it is coming to 155 ppm. However, if you use RO filter (under the sink), it would be using Reverse Osmosis (RO) process to remove above contamination as well as (some good) minerals. Since your PPM is high, the tap water is hardened with lot of minerals (many of them are good) and when it goes through RO, it remove all these minerals and giving you low ppm count. You would be OK to use tap water itself. Refrigerator filter isn’t adding much new value for you — IMHO.