I grow hydro, usually run a full cycle at or below 600ppm in my solution. When it goes in, some amount of the ppm remain in the root zone, some salts dissolve and rinse out, and ultimately the runoff is the same or less as what I pour in.
Generally the pH of the runoff is the same or slightly more acidic than what I pour in.
If you're in the 800s with a sick plant, you have very hot medium. If your runoff is the same or more pH than what you pour in, you have high pH.
Those are the problems I referenced...from here, consider your soil "fully charged."
Feeding only pH adjusted water will allow you to see where things are trending, then only add more if and only if you see clear signs to do so.