They are getting sunburned. If you are overhead watering when the sun is up, the result could be sunburn. If you didn't harden them off well enough, that also will cause sunburn. If the latter, the new leaves will be fine but if the leaves are getting wet when the sun is out, the new leaves will burn also.
Don't fertilize until you get a handle on this problem. And if you fertilized and then the leaves started showing these symptoms, that's a different kind of burn.