Nutrient issue or pests?

Coco coir -- was it prepared well? low EC and buffered with Ca and Mg? if not, disregard below and work on fixing the cation exchange site ratios -- dial down on K, as it's going to be released as the coir locks up the Ca and Mg ions (cation - positive ion, anion - negative ion). if the issue halts, resume normal feed as the coir has reached a better equillibrium with your fertigation. claw, tip burn.. probably too many nutes or something is out of balance. this is the safer path, and you need to adjust if you see it not respond well. First, ensure pH is proper. Check your labels of what you provide and calculate ppms. this will help deduce what is wrong (nute spreadsheet linked in my GD profile comments along with a leaf symptom chart and other good stuff). Have an EC meter? check runoff.. if you find there's plenty of nutes provided, you know it's not a deficiency for sure. dial back. observe and react... potentially a Ca def, but it's only 3 weeks old... if it is, it's likely due to poor prep by manufacturer of your coco coir and soon to be a k-tox too, possibly even salinity issues..