Almost zero, theres still organic matter in the soil which is going to be broken down by the plant and then consumed. The ppm your flushing out is the fertilizer "salts" that youve added. Since organic potting soil has enough nutrients contained in its organic resources to kkep the plant going for usually three weeks you shouldnt have to feed for a while. Ppm meters are usually for adding to the soil, some guys just use them to see whats coming out as well as going in. The most important thing to remember from all this is that the soil grows the plant, not the nutrients you add by themselves. So its fine to water, water, feed if your in soil, not feed,feed,feed,water.