It looks like you answered your own question.Saturday when I got my PPM meter that reads up to 1900, I checked the water and it read 1900+ so I emptied the res, refilled, added nutes until it was at 1100ppm. Sunday Night, I dropped it from 1200 to 740, noticing the plants were not looking healthy.
This morning I dropped it to 400, and foliar fed with just water (ppm 120 / ph 6.0)