If it started on the newer growth then worked its way downwards it’s a zink issue. It’s caused by other elements like calcium and mag being locked out (in my case it was a pH issue causing the lockout). I grow in rdwc so for me it was just a matter of dumping my rez, resetting everything using a pH meter that had been freshly reconfigured. In organic soil it won’t be so easy. Try flushing with PhD water and throwing some calmag at her 
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