I agree with iron deficiency to a point. pH should fluctuate sometimes to allow different nutrients to be absorbed by the roots. The middle of the leaf is yellowing due to iron deficiency, the tips also look like they're yellowing in one of the pictures which is nutrient burn, too many nutes, but since iron is short, I agree with the pH assessment. If it hasn't fluctuated throughout the growth, it's getting the same nutrients over and over and can't get the others.
If you aren't adding anything to your water, do you have any idea what the EC of your water is? Or the EC of the medium? If not, I'd just drop your pH down to 6 and slowly raise it a point each watering to find the "sweet spot" for that particular soil mix.
Not sure how you drilled that half hole out, but if you are watering this amount of soil (in a 5 gal. bucket) for that size a plant, then maybe (not sure) you have been adding nutrients and supplements to the medium (soil) along the way....and, if this is the case the roots have made it out to the hot medium you have created by feeding nutes before they were needed.... in other words, you have created a hot bed for your plants to grow into.....maybe a good flush now will help the plant to rebound 
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