Capsicum leaves dry and curled inwards | Vegetable gardening | Hydroponics farming in India

I am completely puzzled what's causing my capsicum leaves to have brown spots and curl up.
It's getting enough sunlight, water (twice a day).
The plant and the capsicum fruit growth seems to be stunted. I don't see it improving or drying up (leaves falling).
All three of my Bell pepper plants have this. Only one of them seems to be recovering.
I also tried not watering one of the plants for 2 days. No change.
Here are some pics of the leaves.