Ilness or deficency?

Check the PH first before you do anything. Then check run off for salt build up- if those are fine then its likely nute burn from this.. keep this in mind, if you dissolve nutes in water and give it to your plants the coco sucks it up and if you allow all the water to evaporate then all that is left is super strong nutes in the coco. Your best bet if you check PH and its fine is to run 2 times your pots volume (so 10 ltr pot =20 ltrs of water) of either plain water that has been PH to about 6-6.2 or a very weak 1/3rd strength nute solution thru it. That tends to fix most minor probs but dont allow coco to dry out fully as its very hard to re wet in one go. And just go easy on the feeding for a week before bringing it back up near normal.