A conductivity meter or TDS pen can be purchased for a few euros on the main online sales sites. These meters are misleadingly presented as water quality testers, whereas they only allow to show the more or less good conductivity of the water. The conductivity of water is directly proportional to the quantity of solids dissolved in the water, i.e. mineral salts in their ionic form (and not organic matter or various pollutants). Thus, the higher the concentration of dissolved minerals and trace elements, the higher the conductivity. These devices do not detect the presence of pollutants or contaminants. The concentration indicated by these tools before filtration therefore corresponds solely to the content of minerals dissolved in ionic form in your water. The fact of having the same measurement before and after filtration means that the mineral salts have not been retained, which is the very principle of Berkey filtration. This measurement in no way questions the effectiveness of the Black Berkey filters and is not evidence that your system is malfunctioning.
If your measurement is higher after filtration, it means that the filters have not been cleaned properly and that some residual dust remains after the filters have been machined. It will tend to decrease over time.