
hmmmm, need to verify a few things: brand of coco, and did you rinse/CEC buffer it and are you sure your pH meter is calibrated,..and any EC/TDS reading on run-off? I find it weird as hell that the fed went in at 5.8 and r-o was 6.4! Oh, the rainwater, can't be EC 5-

... did you mean 0.5? Even that is pretty ion loaded for such type water,....could have collected stuff while draining.... Do you do 15-20% run-off each time? Did this happen after the feeding? ... something is wack here, you have only fed once in this coco, how old is the plant? Coco is barren stuff, just some native K and Ca/Mg from CEC buffering by the maker,....
Actually, please go to the colored section above this one and find that patient form; copy/paste into here and fill in details for proper diagnostics