Join Date: Jul 2010
Location: Outside Philadelphia, PA
What are the units of your measurements?
4 ppm is a lot different from 4 degrees GH or KH
If your just using an RO system, then a reading like your seeing is possible. If your using an RO/DI system then you should get 0 for GH and KH.
You may have something not quite right with your RO or RO/DI system, for example a filter may not be seated correctly or the restrictor clogged.
If you really get into this area, a TDS meter can help a lot. Some can run inline so you can monitor the water in verses the water out.