Can you provide images with better quality and some more details, e.g. the whole plant, undersides, bottom leaves, top leaves, etc.?
With that pic alone it's hard to diagnose any problems you have.
It might be: (from most probable to least)
- Heat stress/ dry stress
- Overwatering
- Potassium deficiency
- Pests (aphids, etc.)
- Overfertilization (if you added mineralic fertilizer)
- Bad water quality (chlorine, dissolved minerals, cold shock)