Have you been spraying them a lot? This dilutes the nutrients on the inside of the leaves, and if they are diluted too far they become yellow and do not recover.
The first picture looks like an early magnesium deficiency, but the whole plant looks like it has an N deficiency. Do you have a lot of little bugs flying around? If so you have thrips and should get some Spinosad (used 3 times, 5 days apart). If you have to spray with Spinosad make sure you include a 20% solution of grow in the mix, since your leaves are already displaying signs of deficiency.
The only other issue I could see is too much light, but as this is affecting your lower leaves I am ruling this out. My guess would be thrips, and if it's nutrient-related then it's a combination of N and Mg, possibly due to too much foliar spraying.