I don't know, it just really does not strike me as a K or P deficiency.

If you like, go ahead and do a light foliar feeding with a bloom nutrient that contains micros and is mixed MUCH weaker than the bottle recommends. I don't think you should foliar with a grow nute, as you appear to be totally fine on N and don't want to overdo it.

Those drying tips and the slight tip scorch in the pics of the individual leaves really make me think that you've got some type of salting issue there. But it is not severe by any means.

Now is a time to work on prevention of future problems:
With coco, feeding to a slight runoff each time (about 10% is standard) is a good idea. This gives you a constant but slight flushing effect and helps prevent medium salting. Have you tried doing a comparison of the pH/EC going INTO the coco vs the pH and EC coming OUT of the coco? I'd check those numbers. If the 'out' EC number is equal to or higher than the 'in' number, you have cause for concern.