I have a 400 watt MH a friend gave me a 400 watt HPS my hood is a good size so I am going to put both in the same hood . So should I get conversion bulbs and run 2 400 watt MH for veggie grow and 2 400 Watt HPS for flowering or just run 1 400 watt MH and 1 400 watt HPS all the time.
This is a matter of personal opinion, but I would probably just run two HPS bulbs. Im assuming you are going to have a common 2-4 week veg cycle then the rest flowering so save yourself the hassle of changing bulbs. You wont see any huge differences in using MH and switching over to HPS bulbs.