I had similar issues growing with promix. In my environment it would just hold water way to long causing root issues and looking just like yours. I had to switch up to growing with COCO to avoid the overwater or long dry outs. I've just started using gia green as well, so I dont think there is much you can do with the Nitrogen situation and dry amendments already in the soil. I'm no expert but the "root" cause of the deficiencies you are seeing might stem from the over watering/saturation situation causing a lockout rather than a too much or too little of something. Good luck.
(edit) it might help placing your plants on a wire rack or something similar to help dry them out on the bottoms faster.
(edit) it might help placing your plants on a wire rack or something similar to help dry them out on the bottoms faster.