Just coming over here from one of your questions in the noob thread.
Go led instead of HPS if you can afford it, but saying that how big is your space L" X W" ? Just so i can give a better recommendation, from what i see and am guessing a new good quality LED light in the 100-150w range which are $80-120 would likely rock that 400w HPS your running which im guessing is on a magnetic ballast, will reduce heat significantly as well which also meas less exhaust airflow needed.
… and flip whenever as its already filled out area wise, there gonna be fighting 2 week from flip anyways at this point.