If you can and I know your on a budget. Get the biggest ballast you can. There are some good deals. You can put any size bulb you want in a ballast as long as the ballast is equal or bigger. One bro run a 250hps in a 400 ballast am another runs a 400mh in a 1000 switchable ballast for veg.

Later on if you want to exspand your setup it would be easy to just get a bigger bulb. You will thank yourself and if you want to get rid of it later for some reason I find the bigger lights are easier to sell.

Remember the hotter the sun the more TRICHOMES.