to OP, looks like what happens when little tiny bugs suck the juice out of the back of the leaves. Turn the leaf over and look very carefullly. Magnify glass if you have one.
The other thing is that spray fertilizers generally don't have any Iron, magnesium, manganese etc. Try fertilizing with a granular two or three times a year, look at the element content. If you can find one with 1% iron, it will be a bit pricy, but worth it.
When do you usually harvest?