browning tips please look

What can cause this ??? heat nutes or what i use fox farm nutes witch is like 6-3-3 and super thrive and water only when needed this far in i can tell when my plants crave food and they get it about every time i water i got a 400w MH on them about 8 to 10 inchs away maybe less take a look and please give any advice you know.

input plz

Keep the temps around 25-30 degrees celcius and a humidity of 40 procent at that stage. and how close are the lamps to the plants?