First Time Grower

Hi everyone, i've succesfuly managed to grow 5 different female plants and am about 5 weeks in. The largest of all 5(blue widow) looks incredibly healthy but its newest leaves up top have begun to curl upward??? perhaps due to high heat? i just started adding earth juice organic nutrients about a week ago. could this be it? temps in grow room range from 77f to 91f on real hot days. fortunately temps are dropping at the moment outdoors so is the temp of my grow room. ptallest plant was about 8 inches away from a 400w mh lamp.. i just recently raise it 18in above tallest plant and have directed airflow from a small oscilating fan away from hitting the leaves directly. anyone have advice?? please help