I've ran into some problems because I fed the coco plain water at first... (this turned out to be a terrible mistake)
The rootzone pH turned out to be 6.4 and the EC was only 0.4 this caused the weird burns on the leaves
After I found out the issue I flushed it with 5.7 PH and 0.8 EC and since then they have recovered and new healthy green leaves started to form.