This was the most annoying thread I've ever read. Next time listen to those with more experience. Do the damn tests. Choose one or two plants, and try watering them different, in this case water one more often, and water one way less often than your standard watering for the rest of the plants. That is what you should have done. Why ask for help and not use the advice. The advice was good. Your plants suffered so much needlessly.
The problem was most likely how to transfered to coco from soil. First, you should have let it dry out until very light, then remove the whole root ball with soil, gentile shake it to get as much soil of as possible. Then you should have flushed your soil very well, Then you should have sterilized your bathtub, then filled it with luke warm water about 70 degrees, then PH'd to 6.0, then place the whole root system in there. Jiggle it for a while until most of the soil is removed. Wash hands well before getting started.
Then you should have used a good transplant agject, like B1 or super thrive, or something recommended by the hydro shop. Also, mykos does wonders for roots. You should have transplated right after it was lights out for them, so they have all their night to readjust. If you didn't, you should have leaked the coco before using, then after it is in a pot, soak it well with Ph'd water 6.0-6.2. Then you should have waited until it was bone dry, super light to pick up before watering again. This time with 200ppm and ph 6.0. Wait again until bone dry, even so dry some leaves start to droop, or at least stop standing at attention. Then water again but with 400ppm 6.0, then next wating at 600ppm, etc, until you find out what they like. I wouldn't go over 1100ppm. Most likely even at 900 so soon, they would start showing signs of burning.