With my 400w HPS the plants must be at least 24 inches from the light so they dont burn.. If your ph is high, that very well could be the problem. Last week my plants were less than 2 feet from my HPS and I found that my soil was very high in nitrogen. The leaves were dropping and getting little yellow spots especially around the tips and edges. The old leaves started getting very dry and the newer leaves were quickly starting to. I lowered the plant away from the light to a little over 2 feet and flushed my soil with lots of plain water and let it all run out of the bottom to get rid of some of that excess nitrogen.. my plant perked up again and the growth rate exploded, maybe you should try it

-Dr. Nomad
Doc Nomad Reviewed by Doc Nomad on . Urgent please help quick I have 10 4 week old plants. They are bag seeds that ive been growing outside last 2 years pretty kick ass.Anyways thae problem im having growing in soil 1part perilite 1part potting soil and 1 part manure plants were thriving week ago.My temp light on about 85 and off about 70 humidity light on about 45 and off about 55.I transplanted about a week ago because plants looked droppy and leafs felt crispy. I was under 250watt hps about 12" away didnt burn hand.So then i purchased 400 watt hps Rating: 5