How long have you had them under hps? The the leave drooping could be from that. Or it could just be your plants need a drink of water. When your plant leaves start to droop like that usually your plants are screaming "Give me a drink please!" lol.

My guess as the leaf tip burn is either your grow area is to hot(whats the temp at the top of the plants) , or there is minor nute burn (whats you feeding schedule and what strenght and fert do you use).

Your plants should be under 18-24 hours of light to Veg them , and 12/12 cycle to flower them (with 12 hours of complete darkness no light leaks).

I would throw in one of those 125 watt cfl's in the flower chamber to balance out the spectrum better and give them more light more light is always good, and plants like mixed spectrums. Just have more of the reddish spectrum during flower (2200-2700k) , more blueish spectrum (5000-6500k) during vegg.