Realising that this is an old post but looks alot like a deficiency (minor) of some description if it's moving from the bottom up, the edges of the leaves are going too not just the tips which would indicate usually a deficiency over a case of nute burn. The rezin won't have any effect what so ever on what's going on here is an additive used to increase essential oil production. My two cents is you've got a magnesium deficiency which is all too common in coco and you're running down at 5.9 ph and magnesium is pretty much out of range once you go under 6.1 so you've been slowly flushing it out of the plant. The other thing that comes to mind that can present like this is a root problem, have you checked the roots?