It appears that your leave is burnt. There are two possible scenarios here:
The sun (heat) is hurting your plants - Solution: Place a 20-25% shading net on top of them and a fan to provide a gentle breeze.
Nutrient Burn: You are feeding them a lot - Solution: For the next 2 waterings, feed them only water and after that mix a solution with 1/4 of the recommended dosage (for example, if the label says 2ml per liter, insert 0.5ml).