the droop

Now why do they look perefect through out the 18 hour light cycle but towards the end the leaves droop. Then at the beginin of the next cycle they are back to normal. No nut burns or anythin gthey look healthy.

How often does your pump come on? Maybe need to add another water cycle in there. Or remove one.

A picture says a thousand word. It will get you more help but it sounds like RedEye69 may have your answer. Please give us more info on what type of system and light.

I've had my plants do that in the evening...as long as they bounce back in the morning I've been told not to worry about it....they are just resting their leaves at night. The first time I saw some plants do that I flipped out....then next morning they were right back on beam. Interesting isn't it?

I agree with WH I've noticed mine do the same thing...in my experience I linked my drooping leaves before "sunset" to a nute problem

I run an aero9 and I'm at 6 weeks flower 1050ppm at 5.2ph I tried to go higher but the plants just aint havin it with sucha low ph...but growth is looking very healthy so I'm sticking with it...I noticed mine get really dark green and in the cola leaves were curling and they wouldn't reach as much for the light if ppm was higher...

I'd say if your leaves look and feel healthy including the top of the cola yer probably just maxing out the nute intake so it's not the end of the world don't worry unless the leaves stop coming up ;-)

I noticed recently in the last 2 weeks of flower that the ph is dropping faster over night and being relatively stable during the day so I've dropped in 3 hours into the dark to ph up to 5.2-5.3 and 3 hours before light to ph up again to 5.2-5.3