As you're well into flower I wouldn't want to feed too much nitrogen even if there's some yellowing starting. While this is early for the fade to be setting in it's encouraging that you're still seeing good growth. So long as you keep up the nutrients the growth hopefully continues, but you probably won't get back to a good green before the end of harvest. As your grow setup is soilless and your earlier veg pictures look like coco if you're going to check your runoff to see pH, also check the EC.
The buds are looking nice and frosty!
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