Im no pro, but from everything I read.. veg plants need blue spectrum. thats MH lights. Flowering needs Red spectrum. thats HPS lights.

But im sure u can use either all the way through, not with as good results as with a hps for flower. also flowering is the most important thing right? Then personally I would want the best light for flowering which is HPS. so logically if i only had one bulb to choose from. I would go with HPS all the way through.

I went with a switchable ballast so i can use MH or HPS.

Im far from an expert... But thats what ive read.

p.s. plants look good though. keep it up. and im hoping for tight nugs for u with MH all way though. will be good test