It looks like a nutrient deficiency. It could be a pH lockout, This could be from the pH in the water you feed it or the pH changing in the soil over time. Sometimes you can have minerals from the water alone build up to the point of inhibiting or locking out other nutrients.
The pH of the water you use, pH of any nutrient mixtures you use and pH of the soil itself would help confirm or rules these out. A electrical conductivity (EC), or total dissolved solids (TDS) reading of run-off from the soil would give us a idea of what the parts per million of dissolved solids your soil contains and this could give us an idea if there is a nutrient or mineral salt build up contributing to the problem. Also a reading of the PPM of the water alone would help us know if that is a contributor as well.
Check out the support ticket questions and answer the rest of the questions and maybe with more infor we can determine exactly what is going on.
It does not look like light burn or bleaching at all. For one thing light bleaching would most likely be at the top, nearest the light. This appears to be on lower leaves, more indicative of something building up over time.