I am not an expert..... It could be fertilizer burn?? A little more info will definitely help the experts answer your question. Where are you growing (what zone)? What kind of soil are they in? How much sun do they get? How much water and ferts?? Any herbicides used in the vicinity?
The guys and girls here have been very helpful to me but they NEED info to narrow things down.

dj

My guess is bacterial spot.> pepper leaves bacterial spot

It looks like chlorosis to me. That is caused by overwatering and/or a perched water table - where the bottom part of the planting medium is essentially waterlogged even when the top gets dry.

Or it could be a magnesium deficiency. This could be caused by high soil pH. Test your soil pH and apply dolomitic lime as it is indicated.

In the short term you can address a magnesium deficiency by applying some epsom salts. But its unlikely even if this is a magnesium deficiency that its being caused by lack of magnesium in the soil. It is more likely a result of overwatering or soil pH that is too high.