weak stems in a drip system

I started my seedlings 2 weeks ago under 400HPS lights with good ventilation in a hydro drip system (the rainforest). The germinated seeds were transferred into "rapid root" medium which then was inserted between hydroton. The drip system works 24 hrs/day. Yesterday the stems gave way to the weight of the leaves and all my plants fell over. The root system looks good. The light is about 24 inches above. Should I lower my light to 14 inches (gradually), or should I put a more direct fan on my babies? Is it possible they are getting too much water, because the medium never dries out? or shold I build up the hyrdoton to hold the stems up?

Any help would be much appreciated!