Backyard Aquaponics
A place to discuss aquaponics

hi all. im growing a bed of chye sim. everything is looking great. but theres a few of them getting yellow leaves 1/2 leaf...my ph is about 6.9 nitrate is about 70 ish ppm.
this is grown on gravel bed .

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I'm not sure what you've got going on. If it's the older leave turning yellow, I'd try spraying with seaweed extract like Maxicrop or Seasol mostly for the potassium. If it's the younger leaves then spray with an iron supplement.

This is a very nice flowchart for identifying nutrient deficiencies:
http://landresources.montana.edu/nm/documents/NM9.pdf

Scroll to the 6th page and just follow the questions. I would also say this is a iron deficiency.