Soil runoff is basically meaningless. What gets me is the people who's plants look just fine but then they decide to check the runoff for pH and EC. They freak out when the runoff falls outside the parameters they think it should be. Now remember that their is nothing wrong with their plants but they become obsessed with the runoff. They then start dumping tons of water through their pots trying to get the runoff to match what they think it should be. After that their plants start going to shit so they flush them some more. In the end all they did was cause their plants unnecessary stress and end up with crappy plants and a piss poor harvest. I see it all the time on this site and others. Usually when you point out the error of their ways they ignore you and instead listen to some newbie posting some chart of plant deficiencies and telling them to flush with a CalMag solution.