I dont see any point in switching back to an MH bulb now, as dual spectrum is using both simultaneously. Both MH and HPS will veg and flower plants just fine - some people have preferences.

If you can add the MH into the setup as it is now, then you should definitely see the benefit - but I don't think I'd worry about swapping them at this point
Tokudai Reviewed by Tokudai on . swapping out HPS 400w for MH while flowering.. I currently am in week 4 of flowering. I have read many times that running both MH and HPS at the same time is optimal for plant growth through the plant's entire cycle. I have a 400W HPS bulb running to emit the red spectrum right now that I was considering swapping out with my other metal hailide bulb that I started with during veg. My question is: would switching back to a metal hailide bulb at week 4 in flowering do more harm than good or could it possibly make the buds more compact? - Rating: 5