Well, your plants look very healthy. I grow organically and typically when he big fan leaves are drooping its due to environmental issues. I would check the atmosphere and water them. The first sign of under watering is the big fan leaves droop when they usually should be praying. I say "usually" because it depends on what time this picture was taken. Big fan leaves droop right before lights go off and pray when they first come on. Environment check, ensure they don't need watering and go from there.
Best of luck man!