I had the same problems with the yellowing of the leaves and i cured it by giving the soil some magnesium..via "epsom salts" and stopped over watering them as i was doing this as well as this can cause yellowing.

Arthur.

Yellowing leaves is usually down to one of 4 things:

1. Overwatering
2. Underwatering
3. Nutrient Imbalance (too much Nitrogen based fertiliser)
4. Too much sun

Is it just one or two leaves or the full plant?

Mark

The older leaves turn yellow and fall off; normal.
Yellowing of the upper surface may be an indication of insects on the underside. Take a close look.
The upper margin of the leaf in the photograph looks brown and the same might be the case of the lower edge. (I cannot tell). The symptom appears to be progressing from the leaf tip towards the base. If the leaf tends to feel crisp that might indicate a drying out. If the margin symptom is present and the leaf feels OK and especially if it droops, that might indicate too much water. You know what the recent history has been and you can make a diagnosis of the problem based on that. Peppers prefer a dryer soil environment and a good plan would be to withold water until the plant shows that it needs it.

other problems are too much salt or round up

how do you give them epsom salts as my soil is covered in plastic could you dissolve it in water