Certified GKH Gardening Expert
It sounds like blossom end rot, which is caused by a lack of magnesium and calcium. It may not be a true lacking of these elements, though. Sometimes, too much of other fertilizers will lock them out from the plants. Make sure that your fertilizer pads are not nitrogen rich, but do have quite a bit of phosphorus, and potassium, with some focus on calcium and magnesium, as well.
The best way to know for certain is to test your nutrient levels and pH levels, among other things:
Calcium foliar spray may help: