Fill up the res with just plain tap water at correct pH, and some cannazyme if you like (recommended).
Raise your lights.
Run the system for a couple flood cycles, then drain it out and do a complete res change. You can but the res back empty and use a pitcher to pour pHd tap water through the medium to wash down any remaining salts. Of course, dump this too before re-filling.
Now right away go back to a moderate level of your normal ferts.