Weird problem help please

image.jpg image.jpg have this sick AK47 plant and a bunch of questions for you guys but first here is a picture tell me what you guys think.... I'm growing in coco
 
Flushed continuously for about an hour with very low pH and the pH runoff through that entire time never got below 6.0 even if I were to continuously flush with like 4.9 pH water the runoff was still 6.0.
 
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