Yeep! Kinda looks like you HAD a Zinc def if you were seeing that symptom when the leaves were young. Looks from here as if there was a point in time, about a week long, where all the new growth was affected by the problem, but then you see greener growth... Is it getting worse? Are the new leaves setill showing it? The pics seem to show that your new growth is not affected, which indicates the problem no longer exists. It's usually caused by high pH actually- your low pH may have solved it, if new growth looks okay.
Get on those bitches with a micronutrient supplement foliar feed - GH micro- mixed a bit weak, and add one DROP of dish or hand soap to the spray bottle.
Keep us posted, and still try to improve your drainage!