Consider dropping that number (1300ppm) even more for a few days to ease the stress on the plants. Your dots sound like lockout conditions causing a potassium def but I am certainly not positive without seeing photos etc....

Here is a very good sick plant guide. Give it a look through......great useful info in here.

Revised: The Complete Guide To Sick Plants,pH and Pest Troubles - PlanetGanja.com

Good luck.