What is your feeding schedule?
Do you feed to run off?
I grow in coco and never have to go over 600 ppm's..........athena recommends high ppm's because they sell you more nutrients that way.
They look fried to me.......there could be any number of reasons. More info about your grow is required.
You might consider flushing the crap out of the coco with a mild nute solution using a pH around 6,0.
Then start feeding twice a day to substantial run off, using a ppm around 600.
You can't...
Coco and soil have different pH and feeding requirements.
Coco - 6.0 and Soil - 6.5
Coco should be fed daily to run off and kept saturated.
Soil must go through a wet/dry cycle.
I have yet to see a successful grow using a coco/soil mix.
Good luck.
I have always found cocoforcannabis.com to be very informative. It's not a forum like this one.........it's more of a "how to grow in coco" tutorial site.