@Pan the man
Well..listen to me...and you will solve it the problem..
1) Keep it in veg till it will be perfect again.
2) Flush till the run off drop down where you want it.
3) When the run off is where you want, try to keep it there via watering and feeding..When you water or feed is totally dependent on how much they eat..run off will indicate you for this..if you have a run off more than 0.5 of what you put in, water it with plain phed water and check the run off again.
4) Use the right nutrition line for veg.
5) EC for Veg in COCO(not pre-VEG): 1.3 - 1.8 based on the size and the age of the plants. Nothing more.. and nothing less..
Do this every time you feed and water..
This is the only way to save your plants..
Let them in veg, do what i told you, and you will be fine..give it cal mag once a week..you will need it in coco.
Once you see the plants are healthy and thriving again..turn the into flowring..
This info is gold for a coco grower..!
Good luck bro..I wish i helped you!
E.C.