From my experience, the only thing that will lower the ec in a soil type substrate is;
Pure Water with a tds/ppm of 0. This will be either, Distilled Water, Reverse Osmosis Water or De-Ionized water.
Pure water does a good job a stripping nutrients but it will take time to do so. The plant has to feed on what’s in the soil, the 0ppm water will just guarantee you are not adding to EC of the soil.