Drooping leaves ALL the Time

Why are my leaves always drooping???

i have 2 sets of babies, 5 in soil and 4 in clay pebbles,

the 5 in soil are in very good condition,

BUT the 4 in hydroponics (clay pebbles) are drooping all the time and its getting worse????

they are on a drip feed system, (constant watering)

they are 4-5 weeks old, (from seed)

the PH is 6

the EC is 400ppm because i overfertilised them about a week ago and the leaves went yellow, since then they have grown new leaves and they only show slight signs of yellowing at the tips of the leaves,

the temp is abt 24-25 in day and 17-18 at night (humidity ranges between 30-40)

any ideas????

HELP NEEDED??

Over watering will cause the droop. That and a high humidity.

should i set water pump on timer?? off at night??

I dnt know that. It sounds like a way to cut down on watering.